Display device

ABSTRACT

A display device with improved viewing angle characteristics is provided. A display device with suppressed mixture of colors between adjacent pixels is provided. The display device includes a first coloring layer, a second coloring layer, and a structure body therebetween. The structure body has a portion closer to a display surface side than a bottom surface of the first coloring layer or a bottom surface of the second coloring layer.

TECHNICAL FIELD

One embodiment of the present invention relates to a display device.

Note that one embodiment of the present invention is not limited to theabove technical field. Examples of the technical field of one embodimentof the present invention disclosed in this specification and the likeinclude a semiconductor device, a display device, a light-emittingdevice, a power storage device, a memory device, an electronic device, alighting device, an input device, an input/output device, a drivingmethod thereof, and a manufacturing method thereof.

Note that in this specification and the like, a semiconductor devicegenerally means a device that can function by utilizing semiconductorcharacteristics. A transistor, a semiconductor circuit, an arithmeticdevice, a memory device, and the like are each an embodiment of thesemiconductor device. In addition, an imaging device, an electro-opticaldevice, a power generation device (e.g., a thin film solar cell and anorganic thin film solar cell), and an electronic device each may includea semiconductor device.

BACKGROUND ART

Display devices using organic electroluminescent (EL) elements or liquidcrystal elements have been known. Examples of the display device alsoinclude a light-emitting device provided with a light-emitting elementsuch as a light-emitting diode (LED), and electronic paper performingdisplay with an electrophoretic method or the like.

The organic EL element generally has a structure in which a layercontaining a light-emitting organic compound is provided between a pairof electrodes. When voltage is applied to this element, light emissioncan be obtained from the light-emitting organic compound. With use ofsuch an organic EL element, thin, lightweight, high-contrast, andlow-power-consumption display devices can be achieved.

Patent Document 1 discloses a flexible light-emitting device using anorganic EL element.

REFERENCE Patent Document

[Patent Document 1] Japanese Published Patent Application No.2014-197522

DISCLOSURE OF INVENTION

Viewing angle characteristics are a measure of performance of displaydevices. Poor viewing angle characteristics cause a decreased luminanceor a varied chromaticity to be visible when a display surface of adisplay device is seen obliquely. Hence, an improvement in the viewingangle characteristics of display devices is necessary in applicationsrequiring a wide viewing angle.

Furthermore, display devices are required to have higher definition toachieve higher resolution. For example, as compared to large-sizeddevices like home-use television sets, relatively small-sized portableinformation terminals such as cellular phones, smart phones, and tabletterminals need to have higher definition to have increased resolution.

An object of one embodiment of the present invention is to provide adisplay device with improved viewing angle characteristics. Anotherobject of one embodiment of the present invention is to provide adisplay device with suppressed mixture of colors between adjacentpixels. Another object of one embodiment of the present invention is toprovide a high-definition display device. Another object of oneembodiment of the present invention is to provide a thin display device.Another object of one embodiment of the present invention is to providea display device easily manufactured. Another object of one embodimentof the present invention is to provide a low-power-consumption displaydevice. Another object of one embodiment of the present invention is toprovide a highly reliable display device.

Note that the description of these objects does not preclude theexistence of other objects. In one embodiment of the present invention,there is no need to achieve all the objects. Other objects can bederived from the description of the specification and the like.

One embodiment of the present invention is a display device including afirst coloring layer, a second coloring layer, and a structure body. Thefirst coloring layer and the second coloring layer are apart from eachother. The structure body is positioned between the first coloring layerand the second coloring layer and has a portion closer to a displaysurface side than a bottom surface of the first coloring layer or abottom surface of the second coloring layer.

In the above, the thickness of the first coloring layer is preferablydifferent from that of the second coloring layer.

In addition, preferably, a first electrode is provided to overlap withthe first coloring layer, and a second electrode is provided between thefirst electrode and the first coloring layer. In that case, preferably,a layer containing a light-emitting substance is provided between thefirst electrode and the second electrode, and the distance between thesecond electrode and the first coloring layer is partly greater than orequal to 0 μm and less than or equal to 20 μm.

Also preferably, an insulating layer covering an end portion of thefirst electrode is provided, and the structure body is formed over theinsulating layer. In that case, the second electrode preferably has aportion covering a top surface of the structure body.

In addition, the layer containing the light-emitting substancepreferably has a portion positioned between the structure body and thesecond electrode. Furthermore, a cross section of the structure bodypreferably has a portion in which the angle between a side surface and abottom surface is greater than or equal to 25° and less than or equal to155°.

Furthermore, the layer containing the light-emitting substancepreferably has a portion that is positioned between the structure bodyand the second electrode and is thinner than a portion overlapping withthe first electrode.

The aforementioned display device of one embodiment of the presentinvention can include a third electrode overlapping with the firstcoloring layer and include a liquid crystal between the third electrodeand the first coloring layer.

In addition, a fourth electrode having a slit is preferably providedbetween the third electrode and the liquid crystal. In that case,preferably, the distance between the fourth electrode and the firstcoloring layer is partly greater than or equal to 1 μm and less than orequal to 20 μm.

Alternatively, preferably, a fifth electrode is provided between thethird electrode and the first coloring layer, and the liquid crystal ispositioned between the third electrode and the fifth electrode. In thatcase, preferably, the distance between the third electrode and the firstcoloring layer is partly greater than or equal to 1 μm and less than orequal to 20 μm.

According to one embodiment of the present invention, a display devicewith improved viewing angle characteristics can be provided. A displaydevice with suppressed mixture of colors between adjacent pixels can beprovided. A high-definition display device can be provided. A thindisplay device can be provided. A display device easily manufactured canbe provided. A low-power-consumption display device can be provided. Ahighly reliable display device can be provided.

Note that one embodiment of the present invention does not necessarilyachieve all the effects listed above. Other effects can be derived fromthe description of the specification, the drawings, the claims, and thelike.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B illustrate a structural example of a display device ofone embodiment;

FIGS. 2A and 2B illustrate structure examples of a display device of oneembodiment;

FIGS. 3A to 3E illustrate structure examples of a display device of oneembodiment;

FIGS. 4A to 4C illustrate structure examples of a display device of oneembodiment;

FIGS. 5A to 5C illustrate structure examples of a display device of oneembodiment;

FIGS. 6A to 6C illustrate structure examples of a display device of oneembodiment;

FIGS. 7A and 7B illustrate structure examples of a display device of oneembodiment;

FIGS. 8A to 8F illustrate structure examples of a display device of oneembodiment;

FIG. 9 illustrates a structure example of a display device of oneembodiment;

FIG. 10 illustrates a structure example of a display device of oneembodiment;

FIGS. 11A to 11D illustrate structure examples of an input device of oneembodiment;

FIGS. 12A to 12D illustrate structure examples of an input device of oneembodiment;

FIGS. 13A and 13B illustrate structure examples of a display device ofone embodiment;

FIG. 14 illustrates a structure example of a display device of oneembodiment;

FIG. 15 illustrates a structure example of a display device of oneembodiment;

FIGS. 16A, 16B1, and 16B2 illustrate structure examples of a displaydevice of one embodiment;

FIG. 17 illustrates a structure example of a display device of oneembodiment;

FIG. 18 illustrates a structure example of a display device of oneembodiment;

FIGS. 19A and 19B illustrate an example of a driving method of an inputdevice of one embodiment;

FIGS. 20A1, 20A2, 20B1, 20B2, 20C1, and 20C2 illustrate structureexamples of a transistor of one embodiment;

FIGS. 21A1, 21A2, 21A3, 21B1, and 21B2 illustrate structure examples ofa transistor of one embodiment;

FIGS. 22A1, 22A2, 22A3, 22B1, 22B2, 22C1, and 22C2 illustrate structureexamples of a transistor of one embodiment;

FIG. 23 illustrates a display module of one embodiment;

FIGS. 24A to 24H illustrate electronic devices of one embodiment;

FIGS. 25A and 25B illustrate electronic devices of one embodiment;

FIGS. 26A, 26B, 26C1, 26C2, and 26D to 26H illustrate electronic devicesof one embodiment;

FIGS. 27A1, 27A2, and 27B to 27I illustrate electronic devices of oneembodiment;

FIGS. 28A to 28E illustrate electronic devices of one embodiment;

FIGS. 29A and 29B are cross-sectional observation images of Example;

FIG. 30 shows measured XRD spectra of samples;

FIGS. 31A and 31B are TEM images of samples and FIGS. 31C to 31L areelectron diffraction patterns thereof; and

FIGS. 32A to 32C show EDX mapping images of a sample.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments will be described in detail with reference to the drawings.Note that the present invention is not limited to the description below,and it is easily understood by those skilled in the art that the modeand details can be variously changed without departing from the spiritand scope of the present invention. Accordingly, the present inventionshould not be interpreted as being limited to the content of theembodiments below.

Note that in the structures of the invention described below, the sameportions or portions having similar functions are denoted by the samereference numerals in different drawings, and the description of suchportions is not repeated. Furthermore, the same hatching pattern isapplied to portions having similar functions, and the portions are notespecially denoted by reference numerals in some cases.

Note that in each drawing described in this specification, the size, thelayer thickness, or the region of each component is exaggerated forclarity in some cases, and therefore, it is not limited to theillustrated scale.

Note that in this specification and the like, ordinal numbers such as“first” and “second” are used in order to avoid confusion amongcomponents and do not limit the components numerically.

Embodiment 1

In this embodiment, structure examples of a display device of oneembodiment of the present invention will be described.

The display device of one embodiment of the present invention includes aplurality of pixels. Each pixel includes a display element and acoloring layer for coloring light from the display element. An electrode(e.g., a pixel electrode) of the display element and the coloring layercan be provided to face each other. The coloring layers in adjacentpixels are arranged apart from each other.

In addition, a structure body is positioned between two coloring layersin adjacent pixels. The structure body can be positioned, for example,between two pixels corresponding to different colors.

The display device can have a structure, for example, in which a displayelement, a coloring layer, and a structure body are interposed between apair of substrates. For example, one of the substrates can be providedwith an electrode of the display element and the other substrate can beprovided with the coloring layer, and the substrates can be bonded withan adhesive layer. Here, the structure body may be formed on eithersubstrate side.

The structure body may have a function as a spacer for preventing thepair of substrates from getting closer more than necessary. Thestructure body may also have a function of inhibiting mixture of colorsbetween adjacent pixels. For example, in the case where an EL element isused as the display element, the structure body may have a function ofreducing a leakage current between adjacent EL elements to inhibitmixture of colors between adjacent pixels.

Preferably, the structure body is partly positioned on an upper side(closer to the display surface side) than a surface (bottom surface) ofthe coloring layer that faces the display element. In other words, thestructure body preferably fits between the coloring layers apart fromeach other. Note that the structure body is not necessarily in contactwith the coloring layers, and a space, an adhesive layer, or the likemay be positioned therebetween.

This structure can significantly reduce the distance between the pair ofsubstrates. In addition, the structure can drastically reduce thedistance between the display element and the coloring layer, morespecifically, the distance between at least one of the pair ofelectrodes of the display element and the coloring layer, leading toimproved viewing angle characteristics. Furthermore, light from thedisplay element including light emitted obliquely can be taken outeffectively, reducing power consumption. Moreover, a display device witha small thickness can be achieved.

As the display element, a light-emitting element such as an LED, anorganic light-emitting diode (OLED), or a quantum-dot light-emittingdiode (QLED), or an optical element such as a liquid crystal element canbe used. The luminance of light emitted from or through such an elementis controlled by current or voltage.

Besides the above, a micro electro mechanical systems (MEMS) element, anelectron emitter, another optical element, or the like can be used asthe display element. Examples of the MEMS display element include a MEMSshutter display element and an optical interference type MEMS displayelement. A carbon nanotube may be used for the electron emitter. Asanother optical element, an element using a microcapsule method, anelectrophoretic method, an electrowetting method, an Electronic LiquidPowder (registered trademark) method, or the like can be used.

More specific structure examples will be described below with referenceto drawings.

Structure Example 1

FIG. 1A is a schematic perspective view illustrating a display device 10of one embodiment of the present invention. The display device 10includes a substrate 21 and a substrate 31 which are bonded to eachother. In FIG. 1A, the substrate 31 is denoted by a dashed line.

The display device 10 includes a display portion 32, circuits 34, awiring 35, and the like. For example, a conductive layer 23, which isincluded in the circuit 34, the wiring 35, and the display portion 32and serves as a pixel electrode, is provided on the substrate 21 FIG. 1Ashows an example in which an IC 43 and an FPC 42 are mounted on thesubstrate 21.

A circuit serving as a scan line driver circuit can be used as thecircuit 34, for example.

The wiring 35 is configured to supply a signal or electric power to thedisplay portion 32 or the circuit 34, The signal or electric power isinput to the wiring 35 from the outside through the FPC 42 or from theIC 43.

In FIG. 1A, the IC 43 is mounted on the substrate 21 by a chip on glass(COG) method as an example. As the IC 43, for example, an IC serving asa scan line driver circuit or a signal line driver circuit can be used.Note that it is possible that the IC 43 is not provided when, forexample, the display device 10 includes circuits serving as a scan linedriver circuit and a signal line driver circuit and when the circuitsserving as a scan line driver circuit and a signal line driver circuitare provided outside and a signal for driving the display device 10 isinput through the FPC 42. Alternatively, the IC 43 may be mounted on theFPC 42 by a chip on film (COF) method.

FIG. 1A shows an enlarged view of part of the display portion 32. Theconductive layers 23 included in a plurality of display elements arearranged in a matrix in the display portion 32. The conductive layer 23serves as, for example, a pixel electrode. A structure body 11 isprovided between the two conductive layers 23 adjacent to each other.Here, the structure body 11 is preferably provided between the twoconductive layers 23 included in two pixels corresponding to differentcolors. Alternatively, the structure body 11 may be provided between theconductive layers 23 included in two pixels corresponding to the samecolor.

Cross-Sectional Structure Example 1 Cross-Sectional Structure Example1-1

FIG. 1B shows an example of a cross section along line A1-A2 in FIG. 1A.FIG. 1B shows the cross section of a region including two adjacentpixels (sub-pixels). In this example, a light-emitting element 40 with atop-emission structure is used as a display element; thus, the displaysurface is on the side of the substrate 31.

The display device 10 has a structure in which the substrate 21 and thesubstrate 31 are bonded with an adhesive layer 39. In other words, thelight-emitting element 40 is sealed with the adhesive layer 39.

A transistor 70, the light-emitting element 40, the structure body 11,and the like are provided over the substrate 21. In addition, insulatinglayers 73, 81, 82, and the like are provided over the substrate 21. Onthe surface of the substrate 31 that faces the substrate 21, providedare a coloring layer 51 a, a coloring layer 51 b, a light-blocking layer52, and the like.

The coloring layers 51 a and 51 b are apart from each other. Thelight-blocking layer 52 is positioned between the coloring layers 51 aand 51 b. As illustrated in FIG. 1B, the light-blocking layer 52 and thecoloring layer 51 a are preferably arranged to partly overlap with eachother. The same applies to the light-blocking layer 52 and the coloringlayer 51 b.

The transistor 70 includes a conductive layer 71 serving as a gate, asemiconductor layer 72, the insulating layer 73 serving as a gateinsulating layer, a conductive layer 74 a serving as one of a source anda drain, a conductive layer 74 b serving as the other of the source andthe drain, and the like.

The insulating layer 81 is provided to cover the transistor 70, and theconductive layer 23 is provided over the insulating layer 81. Theconductive layer 23 is electrically connected to the conductive layer 74b through an opening in the insulating layer 81. Part of the conductivelayer 23 serves as a pixel electrode.

The insulating layer 82 is provided to cover an end portion of theconductive layer 23.

The insulating layer 82 preferably has a tapered shape.

The structure body 11 is provided over the insulating layer 82. Thestructure body 11 is positioned between the two light-emitting elements40 adjacent to each other in a plan view. Furthermore, the structurebody 11 includes a portion positioned between the two coloring layers(the coloring layers 51 a and 51 b) adjacent to each other in a planview. The structure body 11 is also preferably arranged to overlap withpart of the light-blocking layer 52 in a plan view.

The light-emitting element 40 includes an EL layer 24 and a conductivelayer 25 which are provided over the conductive layer 23. Part of theconductive layer 25 serves as a common electrode of the light-emittingelement 40. When a potential difference is generated between theconductive layers 23 and 25 and current flows through the EL layer 24,the light-emitting element 40 emits light.

FIG. 1B shows an example in which the EL layer 24 and the conductivelayer 25 are shared with a plurality of pixels. The EL layer 24 coversthe insulating layer 82 and the structure body 11 as well as an exposedportion of the conductive layer 23. The conductive layer 25 covers theEL layer 24.

In FIG. 1B, the structure body 11 includes a portion positioned abovethe surfaces (bottom surfaces) of the coloring layers 51 a and 51 b thatface the light-emitting element 40. This provides a structure in whichthe structure body II fits between the coloring layers 51 a and 51 b. Inthat case, the coloring layer 51 a, the coloring layer 51 b, or thelight-blocking layer 52 is not necessarily in contact with the structurebody 11 (or the surface of the conductive layer 25 covering thestructure body 11), and the adhesive layer 39 may be providedtherebetween as illustrated in FIG. 1B.

Such a structure enables the distance between the substrates 21 and 31to be extremely small. The smaller the distance between thelight-blocking layer 52 and the light-emitting element 40 is, the widerthe angle of light emitted from the light-emitting element 40 through anopening of the light-blocking layer 52 can be. As a result, a displaydevice with improved viewing angle characteristics can be achieved.

In addition, the distance between the light-emitting element 40 and thecoloring layer 51 a can be extremely small; hence, almost all of thelight emitted from the light-emitting element 40 to the display surfaceside enters the coloring layer 51 a. Even in the case where light isemitted obliquely to a coloring layer (e.g., the coloring layer 51 b) inan adjacent pixel, the light is absorbed first by the coloring layer 51a except for a specific color, and therefore is not emitted to theoutside through the coloring layer 51 b. This significantly reduces themixture of colors between adjacent pixels, resulting in a smaller changein chromaticity when the display surface is obliquely seen.

For comparison, FIG. 2A shows an example in which coloring layers of twoadjacent pixels are arranged to overlap with each other to reduce themixture of colors between the adjacent pixels. FIG. 2A illustrates partof a coloring layer 51 c in addition to the coloring layers 51 a and 51b. FIG. 2B is a modification example of FIG. 2A in which the structurebody 11 is not provided so that the distance between the substrates 31and 21 is reduced.

In the structures illustrated in FIGS. 2A and 2B, the mixture of colorsbetween the adjacent pixels can be reduced because the two coloringlayers partly overlap between the adjacent pixels. However, a reductionin the distance between the substrates 21 and 31 is restricted by thethickness of the portion where the two coloring layers overlap, and thedistance cannot be reduced substantially as compared to that in thestructure with the coloring layers not overlapping. In contrast, FIG. 1Bshows the structure in which the coloring layers are apart from eachother and the structure body 11 fits therebetween; accordingly, themixture of color can be reduced and the distance between the substratescan be made quite small. Thus, in the structure of FIG. 1B, a change inluminance from an oblique angle can be reduced more effectively than inthe structures of FIGS. 2A and 2B.

The structure body 11 may have a function as a spacer for preventing thesubstrates 21 and 31 from getting closer more than necessary. Hence, thesurface of the structure body 11, or the surface of a layer (e.g., theconductive layer 25) covering the structure body 11 may be in contactwith a component such as the light-blocking layer 52 provided on thesubstrate 31.

The structure body 11 may have a function of absorbing at least part ofvisible light. This makes it possible to partly absorb light emittedobliquely to the coloring layer in an adjacent pixel through thestructure body 11 and to reduce the mixture of colors between adjacentpixels more effectively. The structure body 11 may be formed using amaterial similar to that for the coloring layer 51 a or 51 b or thelight-blocking layer 52.

Although the display device 10 described here is an active matrixdisplay device including an active element such as the transistor 70, apassive matrix display device including no active elements can also beused. In that case, the transistor 70 is not necessary and for example,components between the conductive layer 23 and the substrate 21 can beomitted.

FIG. 3A is an enlarged view of a region surrounded by the dashed-dottedline in FIG. 1B.

As illustrated in FIG. 3A, h1 denotes the height of the highest(thickest) point of the structure body 11; h2, the height of the lowestpoint of the coloring layer 51 a; h3, the height of the highest point ofthe conductive layer 25 over the structure body 11; h4, the height ofthe highest point of the coloring layer 51 a, i.e., the height of asurface where the coloring layer 51 a is formed; h5, the height of thetop surface of the conductive layer 23; and h6, the height of the topsurface of the conductive layer 25 that overlaps with the conductivelayer 23. Here, the height of a point refers to, for example, thedistance from the surface of the substrate 21 to the point.

As illustrated in FIG. 3A, the structure body 11 is formed so that theheight h1 of the structure body 11 is higher than the height h2 of thebottom surface of the coloring layer 51 a. Similarly, the conductivelayer 25 is formed so that the height h3 of the top surface of theconductive layer 25 over the structure body 11 is higher than the heighth2. Here, the top surface of the conductive layer 25 and the bottomsurface of the light-blocking layer 52 may be partly in contact witheach other.

Distance dl is the distance between the top surface of the conductivelayer 25 and the bottom surface of the coloring layer 51 a in thedirection perpendicular to the surface of the substrate 21. That is, thedistance d1 is equal to a value obtained by subtracting the height h6from the height h2. The mixture of colors between adjacent pixels can bereduced as the distance dl decreases. The distance d1 can be, forexample, greater than or equal to 0 μm and less than or equal to 20 μm,preferably greater than or equal to 0 μm and less than or equal to 10μm, and more preferably greater than or equal to 0 μm and less than orequal to 5 μm. The distance d1 of 0 μm means that the conductive layer25 is in contact with the coloring layer 51 a.

Distance d2 is the distance between the top surface of the conductivelayer 25 and the surface where the coloring layer 51 a is formed in thedirection perpendicular to the surface of the substrate 21. That is, thedistance d2 is equal to a value obtained by subtracting the height h6from the height h4, and equal to a value obtained by adding the distanced1 to the thickness of the coloring layer 51 a. A decrease in luminanceat the time of obliquely viewing the display surface can be reduced asthe distance d2 decreases. The thickness of the coloring layer 51 a canbe, for example, greater than or equal to 100 nm and less than or equalto 5 μm, preferably greater than or equal to 200 nm and less than orequal to 4 μm, and more preferably greater than or equal to 500 nm andless than or equal to 3 μm.

Here, in the case where the distance between A and B is greater than orequal to x and less than or equal to y, a portion where the distancebetween A and B is greater than or equal to x and less than or equal toy only needs to be included in an observed area.

Distance d3 is the distance between the top surface of the conductivelayer 23 and the bottom surface of the coloring layer 51 a in thedirection perpendicular to the surface of the substrate 21. That is, thedistance d3 is equal to a value obtained by subtracting the height h5from the height h2, and equal to a value obtained by adding the distanced1 to the thicknesses of the EL layer 24 and the conductive layer 25.Note that in the case where an optical adjustment layer is provided toachieve a microcavity structure, the thickness of the optical adjustmentlayer is assumed to be included in the thickness of the EL layer 24. Themixture of colors between adjacent pixels can be reduced as the distanced3 decreases. The thickness of the EL layer 24 can be optimized inaccordance with the structure or formation method of the light-emittingelement 40; for example, can be greater than or equal to 20 nm and lessthan or equal to 1 μm. The thickness of the conductive layer 25 can beoptimized in accordance with the material or required resistancethereof; for example, can be greater than or equal to 0.3 nm and lessthan or equal to 1 μm.

The distance d3 between the top surface of the conductive layer 23 andthe bottom surface of the coloring layer 51 a can be, for example,greater than or equal to 20 nm and less than or equal to 22 μm,preferably greater than or equal to 20 nm and less than or equal to 20μm, more preferably greater than or equal to 20 nm and less than orequal to 10 μm, and still further preferably greater than or equal to 20nm and less than or equal to 5 μm.

Distance d4 is the distance between the top surface of the conductivelayer 23 and the surface where the coloring layer 51 a is formed in thedirection perpendicular to the surface of the substrate 21. That is, thedistance d4 is equal to a value obtained by subtracting the height h5from the height h4, and equal to a value obtained by adding the distanced3 to the thickness of the coloring layer 51 a. A decrease in luminanceat the time of obliquely viewing the display surface can be reduced asthe distance d4 decreases.

Next, the shape of the structure body 11 is described. As illustrated inFIG. 3A, a taper angle of the structure body 11 is denoted as a taperangle θ. Here, the taper angle of the structure body 11 refers to anangle between a bottom surface (a surface in contact with the surfacewhere the structure body 11 is formed) and a side surface at an endportion of the structure body 11. The taper angle is greater than 0° andless than 180°. A taper with an angle less than or equal to 90° isreferred to as a forward taper whereas a taper with an angle greaterthan 90° is referred to as an inverse taper in some cases.

The taper angle θ of the structure body 11 is preferably greater than orequal to 25° and less than or equal to 155°, more preferably greaterthan or equal to 30° and less than or equal to 150°, and still furtherpreferably greater than or equal to 35° and less than or equal to 145°.

In the case where the EL layer 24 is shared with a plurality of pixelsas illustrated in FIG. 1B and FIG. 3A, if the EL layer 24 includes ahighly conductive layer, current might flow to the light-emittingelement 40 in an adjacent pixel through the highly conductive layer. Thesame applies to the case where the EL layer 24 includes a layercontaining both a donor substance and an acceptor substance. This causesa problem of lower color reproducibility due to the light emission ofthe light-emitting element 40 in the adjacent pixel, which should notemit light. Such a phenomenon can be referred to as crosstalk.

The taper angle 0 of the structure body 11 in the above range allows theEL layer 24 covering the structure body 11 to be partly thin. Inparticular, a portion of the EL layer 24 that covers the side surface ofthe structure body 11 can be formed thinner than another portion thatcovers the top surface of the structure body 11 or another portion overthe conductive layer 23. The EL layer 24 can also be dividedparticularly when the structure body 11 has an inverse tapered shape.Such a structure body 11 contributes to a reduction in the currentflowing to an adjacent pixel through the EL layer 24 even when the ELlayer 24 includes highly conductive layer or a layer containing both adonor substance and an acceptor substance. As a result, crosstalk can bereduced.

FIGS. 3B to 3D illustrate examples of the cross section of the structurebody 11 and the EL layer 24 and the conductive layer 25 which areprovided to cover the structure body 11.

The structure body 11 illustrated in FIG. 3B has a forward taperedshape, and a portion of the EL layer 24 that covers the end portion ofthe structure body 11 is reduced in thickness.

The structure body 11 illustrated in FIG. 3C has an inverse taperedshape, and the portion of the EL layer 24 that covers the end portion ofthe structure body 11 is reduced in thickness.

In FIG. 3D, the end portion of the structure body 11 has a continuouscurvature to reduce the thickness of the portion of the EL layer 24 thatcovers the end portion of the structure body 11. In the case where theend portion of the structure body 11 has a continuous curvature asillustrated in FIG. 3D, the widest angle between the bottom surface andthe side surface of the structure body 11 can be regarded as the taperangle θ of the structure body 11.

Note that in the cross section observation, the boundary between theinsulating layer 82 and the structure body 11 cannot be clearly seendepending on their materials. In addition, the boundary does notactually exist in the case where, for example, the insulating layer 82and the structure body 11 are formed using the same material or formedwith the same film by using an exposure technique with a half-tone mask,a gray-tone mask, or the like, or a multiple exposure technique. In thatcase, a portion extending up and the other portion can be regarded asthe structure body 11 and the insulating layer 82, respectively. FIG. 3Dshows an example including no boundary between the insulating layer 82and the structure body 11, and a dashed line denotes an example of aline that can be regarded as the boundary.

In the case where the structure body 11 has an inverse tapered shape, asillustrated in FIG. 3E, the EL layer 24 covering the structure body 11is sometimes divided in the vicinity of the side surface of thestructure body 11. In that case, preferably, the conductive layer 25covering the structure body 11 is not divided though it may be reducedin thickness in the vicinity of the side surface of the structure body11. This allows the EL layer 24 to be covered with the conductive layer25 without being exposed also in the vicinity of the side surface of thestructure body 11, resulting in improved reliability.

The above is the description of Cross-sectional structure example 1-1.

Described below is an example of a structure partly different from theabove cross-sectional structure example 1-1.

Cross-Sectional Structure Example 1-2

FIG. 4A illustrates an example different from FIG. 1B in that thethickness of the coloring layer 51 b is smaller than that of thecoloring layer 51 a.

The bottom surface of the coloring layer 51 a is positioned below thetop surface of the structure body 11, and the bottom surface of thecoloring layer 51 b is positioned above the top surface of the structurebody 11. In such a case where the coloring layers have differentthicknesses between pixels, the structure body 11 only needs to bepartly positioned above the bottom surface of at least one coloringlayer.

Cross-Sectional Structure Example 1-3

FIG. 4B illustrates an example different from FIG. 1B in that the ELlayer 24 is separately formed for each pixel. In the structure of FIG.4B, an EL layer 24 a and an EL layer 24 b are provided to overlap withthe coloring layer 5Ia and the coloring layer 51 b, respectively. The ELlayers 24 a and 24 b contain light-emitting substances emitting light ofdifferent colors. The conductive layer 25 is shared with adjacent pixelsand partly covers the structure body 11. Note that the EL layers 24 aand 24 b may be formed without being divided between pixels of the samecolor.

Even in such a case where the EL layers are separately formed, the colorreproducibility of the display device can be significantly improved dueto the coloring layers.

In that case, the structure body 11 may have a function as a spacer forpreventing a mask (metal mask) used for the deposition of the EL layers24 a and 24 b from being in contact with the surface where the EL layer24 a or 24 b is formed.

Cross-Sectional Structure Example 1-4

FIG. 4C illustrates an example in which the EL layer 24 and theconductive layer 25 are separately formed for each pixel.

In the example of FIG. 4C, the surface of the structure body 11 includesa liquid-repellent portion 11 a. Thus, in the case where the EL layer 24and the conductive layer 25 are formed by a method using a liquidmaterial, such as an inkjet method, a dispensing method, or a screenprinting, materials of the EL layer 24 and the conductive layer 25 canbe prevented from spreading over the structure body 11 to an adjacentpixel. As a result, the EL layer 24 and the conductive layer 25 can bepositioned between the two structure bodies 11 as illustrated in FIG.4C.

Although both the EL layer 24 and the conductive layer 25 are formedseparately for each pixel in this example, the conductive layer 25 maybe formed by an evaporation method, a sputtering method, or the like soas to be shared with adjacent pixels.

The EL layer 24 may be formed without being divided between adjacentpixels of the same color. The conductive layer 25 is preferably formedwithout being divided between adjacent pixels in the width direction ofFIG. 4C.

Cross-Sectional Structure Example 1-5

FIG. 5A illustrates an example in which the conductive layer 25 over thestructure body 11 is in contact with the light-blocking layer 52. Partof the conductive layer 25 and the light-blocking layer 52 may be incontact with each other in part or the whole of the display portion 32.When the conductive layer 25 is in contact with the light-blocking layer52 in the whole of the display portion 32, the distance between thesubstrates 31 and 21 is unlikely to vary, reducing display unevenness.

Cross-Sectional Structure Example 1-6

FIG. 5B illustrates an example in which an end portion of the coloringlayer 51 a is covered with the light-blocking layer 52. With such astructure, light traveling through the coloring layer 51 a to anadjacent pixel can be prevented effectively.

Cross-Sectional Structure Example 1-7

FIG. 5C illustrates an example in which the transistor 70 is replacedwith a transistor 90 which includes a semiconductor layer formed in partof a single crystal substrate 91.

The transistor 90 illustrated in FIG. 5C includes a channel region 92, alow-resistance region 94 a serving as one of a source and a drain, alow-resistance region 94 b serving as the other of the source and thedrain, the insulating layer 73 serving as a gate insulating layer, theconductive layer 71 serving as a gate, and the like. The channel region92 and the low-resistance regions 94 a and 94 b are formed in the singlecrystal substrate 91. Furthermore, a separation layer 97 for separatingcomponents is provided in the single crystal substrate 91.

Insulating layers 81 a, 81 b, and 81 c are provided to cover thetransistor 90. A conductive layer 96 is provided over the insulatinglayer 81 a and connected to the low-resistance region 94 a or 94 bthrough a connection layer 95 a embedded in the insulating layer 81 a.The conductive layer 23 is provided over the insulating layer 81 c andconnected to the conductive layer 96 through a connection layer 95 bembedded in the insulating layer 81 c. The conductive layer 96 is formedto be embedded in the insulating layer 81 b, and the surfaces thereofare planarized.

Such a structure enables minute pixels to be formed on the singlecrystal substrate 91, and therefore achieves a display device withextremely high definition.

Cross-Sectional Structure Example 1-8

FIG. 6A illustrates an example in which the structure body 11 isprovided on the substrate 31 side.

The structure body 11 illustrated in FIG. 6A is provided so as to havethe bottom surface which is closer to the substrate 31 side than thebottom surfaces of the coloring layers 51 a and 51 b are.

The coloring layers 51 a and 51 b are preferably provided on the innerside of the opening in the insulating layer 82, which results in asmaller distance between the coloring layers 51 a and 51 b and thelight-emitting element 40.

The structure body 11 is provided to overlap with the insulating layer82. The structure body 11 and the conductive layer 25 may be in contactwith each other or the adhesive layer 39 may be positioned therebetween.

Cross-Sectional Structure Example 1-9

FIG. 6B illustrates an example different from FIG. 6A in that the ELlayer 24 is separately formed for each pixel. The EL layer 24 a and theEL layer 24 b are provided to overlap with the coloring layer 51 a andthe coloring layer 51 b, respectively. The conductive layer 25 is sharedwith adjacent pixels.

FIG. 6B illustrates an example in which the structure body 11 and theconductive layer 25 are partly in contact with each other in a regionoverlapping with the insulating layer 82.

Cross-Sectional Structure Example 1-10

FIG. 6C illustrates an example in which the EL layer 24 and theconductive layer 25 are separately formed for each pixel.

Shown here is an example in which the surface of the insulating layer 82includes a liquid-repellent portion 82 a, and the EL layer 24 a, the ELlayer 24 b, and the conductive layer 25 are positioned on the inner sideof the opening in the insulating layer 82

In FIG. 6C, the structure body 11 and the insulating layer 82 are partlyin contact with each other.

Cross-Sectional Structure Example 1-11

FIG. 7A illustrates an example in which a liquid crystal element 60 isused as the display element. The liquid crystal element 60 includes aconductive layer 61, a liquid crystal 62, and a conductive layer 63. Theliquid crystal element 60 illustrated in FIG. 7A is a transmissiveliquid crystal element using a vertical alignment (VA) mode.

The conductive layer 61 is provided over the insulating layer 81. Theconductive layer 61 is electrically connected to the conductive layer 74a of the transistor 70 through the opening in the insulating layer 81.

On the substrate 31 side, an insulating layer 64 is provided to coverthe coloring layer 51 a, the coloring layer 51 b, and the light-blockinglayer 52. The insulating layer 64 may have a function of preventingdiffusion of impurities, which are contained in the coloring layer 51 aor 51 b or the light-blocking layer 52, to the liquid crystal 62.

The conductive layer 63 is provided to cover the insulating layer 64.The liquid crystal element 60 has a structure in which the liquidcrystal 62 is interposed between the conductive layers 61 and 63.

Preferably, a top surface of the insulating layer 64 is partlypositioned on an upper side (closer to the substrate 31 side) than thebottom surface of the coloring layer 51 a between the coloring layers 51a and 51 b. In other words, the surface of the insulating layer 64preferably has a depressed portion between the coloring layers 51 a and51 b. The structure body 11 on the substrate 21 side fits in thedepressed portion of the insulating layer 64. With such a structure, thestructure body 11 on the substrate 21 side can be positioned to fitbetween the two coloring layers adjacent to each other. This can reducethe distance between the substrates 21 and 31 as compared to the casewhere the insulating layer 64 has a flat surface, thereby improving theviewing angle characteristics.

The structure body 11 serves as a spacer for maintaining a predetermineddistance between the substrates 21 and 31. The structure body 11 allowsan optimum distance between the conductive layers 61 and 63 to be keptin the liquid crystal element 60.

Although not illustrated here, an alignment film for adjusting thealignment of the liquid crystal 62 may be provided between theconductive layer 61 and the liquid crystal 62 and between the conductivelayer 63 and the liquid crystal 62.

The distance between the top surface of the conductive layer 61 and thebottom surface of the coloring layer 51 a or the like is equivalent tothe distance d3 illustrated in FIG. 3A. The distance may be optimized inaccordance with the structure of the liquid crystal element 60; forexample, can be greater than or equal to 1 μm and less than or equal to20 μm, preferably greater than or equal to 1.5 μm and less than or equalto 10 μm, and more preferably greater than or equal to 2 μm and lessthan or equal to 5 μm.

Cross-Sectional Structure Example 1-12

FIG. 7B illustrates an example in which the liquid crystal element 60using a fringe field switching (FFS) mode is used as the displayelement. The conductive layers 61 and 63 in the liquid crystal element60 are provided on the substrate 21 side.

The conductive layer 61 is provided over the insulating layer 81, andthe insulating layer 65 is provided to cover the conductive layer 61.The conductive layer 63 is provided over the insulating layer 65. Thetop surface of the conductive layer 63 has a comb-like shape or a shapewith at least one opening (slit).

The conductive layer 61 is electrically connected to the transistor 70and serves as a pixel electrode. The conductive layer 63 provided overthe conductive layer 61 with the insulating layer 65 therebetween servesas a common electrode. Note that the conductive layer 63 may beelectrically connected to the conductive layer 74 a of the transistor 70through openings in the insulating layers 65 and 81 so as to serve as apixel electrode. In that case, the conductive layer 61 can be sharedwith adjacent pixels and may be used as a common electrode.

When a material transmitting visible light is used for the conductivelayer 61 in FIGS. 7A and 7B, a transmissive liquid crystal element canbe obtained. A conductive material transmitting visible light ispreferably used for both of the conductive layers 61 and 63, because theaperture ratio can be further increased.

In the case where the liquid crystal element 60 is a reflective liquidcrystal element, a material reflecting visible light may be used for oneor both of the conductive layers 61 and 63. When a material reflectingvisible light is used for both of them, the aperture ratio can beincreased. Alternatively, a material reflecting visible light may beused for one of the conductive layers 61 and 63 and a materialtransmitting visible light may be used for the other.

Alternatively, a material reflecting visible light and a materialtransmitting visible light may be used for the conductive layer 61 andthe conductive layer 63, respectively, so that a semi-transmissiveliquid crystal element is achieved. In that case, a reflective modeusing light reflected by the conductive layer 61 and a transmissive modeusing light from a backlight which passes through a slit in theconductive layer 61 can be switched.

Although not illustrated in FIGS. 7A and 7B, a backlight can be providedon the outer side of the substrate 21 or 31. In addition, a polarizingplate can be provided on each outer side of the substrates 21 and 31.

The distance between the top surface of the conductive layer 63 and thebottom surface of the coloring layer 51 a or the like is equivalent tothe distance d3 illustrated in FIG. 3A. The distance may be optimized inaccordance with the structure of the liquid crystal element 60; forexample, can be greater than or equal to 1 μm and less than or equal to20 μm, preferably greater than or equal to 1.5 μm and less than or equalto 10 μm, and more preferably greater than or equal to 2 μm and lessthan or equal to 5 μm.

Example of Arranging Method of Structure Body

FIGS. 8A to 8F are enlarged views of part of the display portion 32 seenfrom the display surface side. Shown here is an example in which thelight-blocking layer 52 is on the outermost display surface, thecoloring layers 51 a, 51 b, and 51 c are provided thereunder, and theconductive layer 23 and the structure body 11 are provided thereunder.The structure body 11, the conductive layer 23, and the like are denotedby dashed lines.

FIGS. 8A to 8D illustrate examples in which the coloring layers 51 a, 51b, and 51 c and the light-blocking layer 52 are arranged in stripes. Thelight-blocking layer 52 and each of the coloring layers partly overlapwith each other.

FIG. 8A illustrates an example in which the structure body 11 with anisland shape is provided between the two conductive layers 23. Thestructure body 11 overlaps with the light-blocking layer 52.

In FIG. 8A, the length of the structure body 11 is longer than that ofthe conductive layer 23 in the longitudinal direction. In FIG. 8B, thelength of the structure body II is shorter than that of the conductivelayer 23 in the longitudinal direction. In FIG. 8C, the structure body11 has a dot-like shape. In FIG. 8D, the structure body 11 is arrangedin a stripe like the light-blocking layer 52 and the like.

FIGS. 8E and 8F illustrate examples in which the light-blocking layer 52has a lattice shape. Here, the coloring layers 51 a, 51 b, and 51 c eachhave an island shape to overlap with the conductive layer 23.

In FIG. 8E, the island-like structure body 11 is provided on each sideof the conductive layer 23. In FIG. 8F, the structure body 11 has alattice shape.

Note that the shape and the arrangement of the structure body 11 are notlimited to the above, and the structure body 11 can be provided so as tobe interposed between two adjacent coloring layers.

Cross-Sectional Structure Example 2

Hereinafter, the cross-sectional structure example of the display device10 of one embodiment of the present invention will be described morespecifically. In particular, a top-emission light-emitting element isused as the display element.

Cross-Sectional Structure Example 2-1

FIG. 9 is a schematic cross-sectional view of the display device 10.FIG. 9 illustrates an example of the cross sections of a regionincluding the FPC 42, a region including the circuit 34, a regionincluding the display portion 32, and the like in FIG. 1A. Furthermore,in FIG. 9, the cross section of a region including a transistor and thelike and the cross section of a region between adjacent pixels are shownside-by-side as the display portion 32.

The substrates 21 and 31 are bonded with an adhesive layer 141. Part ofthe adhesive layer 141 has a function of sealing the light-emittingelement 40, The polarizing plate 130 is preferably provided on the outerside of the substrate 31.

The light-emitting element 40, a transistor 201, a transistor 202, atransistor 205, a capacitor 203, a terminal portion 204, the wiring 35,the structure body 11, and the like are provided over the substrate 21.A coloring layer 131 a, a coloring layer 131 b, a light-blocking layer132, and the like are provided on the substrate 31 side. Thelight-emitting element 40 has a stacked structure of a conductive layer111, an EL layer 112, and a conductive layer 113. Part of the conductivelayer 111 serves as a pixel electrode whereas part of the conductivelayer 113 serves as a common electrode. The light-emitting element 40 isa top-emission light-emitting element in which light is emitted to thesubstrate 31 side.

FIG. 9 illustrates a cross section including one sub-pixel as an exampleof the display portion 32. The sub-pixel includes, for example, thetransistor 202, the capacitor 203, the transistor 205, thelight-emitting element 40, and the coloring layer 131 a. For example,the transistor 202 is a switching transistor (selection transistor), andthe transistor 205 is a transistor for controlling current flowing inthe light-emitting element 40 (a driving transistor).

In FIG. 9, a cross section including the transistor 201 is illustratedas an example of the circuit 34.

Materials transmitting different colors can be used for the coloringlayers 131 a, 131 b, and the like. For example, when a sub-pixelexhibiting a red color, a sub-pixel exhibiting a green color, and asub-pixel exhibiting a blue color are arranged, full-color display canbe achieved.

Insulating layers such as insulating layers 211 to 216 are provided overthe substrate 21. A portion of the insulating layer 211 serves as a gateinsulating layer of each transistor, and another portion thereof servesas a dielectric of the capacitor 203. The insulating layers 212, 213,and 214 are provided to cover each transistor, the capacitor 203, andthe like. The insulating layer 214 serves as a planarization layer.Shown here is an example in which the three insulating layers 212, 213,and 214 are provided to cover the transistors and the like; however, oneembodiment of the present invention is not limited to this example, andfour or more insulating layers, a single insulating layer, or twoinsulating layers may be provided. The insulating layer 214 serving as aplanarization layer is not necessarily provided when not needed. Theinsulating layer 215 is provided to cover a conductive layer 224. Theinsulating layer 215 may have a function as a planarization layer. Theinsulating layer 216 is provided to cover an end portion of theconductive layer 111, a contact portion that electrically connects theconductive layers 111 and 224, and the like. The insulating layer 216has a function as a planarization layer.

The structure body 11 is provided over the insulating layer 216. Asillustrated in FIG. 9, part of the structure body 11 is positioned on anupper side than the bottom surface of the coloring layer 131 a.

The transistors 201, 202, and 205 each include a conductive layer 221part of which serves as a gate electrode, a conductive layer 222 part ofwhich serves as a source or a drain electrode, and a semiconductor layer231. Here, a plurality of layers obtained by processing the sameconductive film are shown with the same hatching pattern.

In the example in FIG. 9, the capacitor 203 includes part of theconductive layer 221 serving as a gate electrode of the transistor 205,part of the insulating layer 211, and part of the conductive layer 222serving as a source or a drain electrode of the transistor 205.

In the transistor 202, one of the pair of conductive layers 222 that isnot electrically connected to the capacitor 203 serves as part of asignal line. The conductive layer 221 serving as a gate electrode of thetransistor 202 also serves as part of a scan line.

FIG. 9 illustrates an example in which the transistor 202 includes onegate electrode. The transistors 201 and 205 are each a transistor inwhich the semiconductor layer 231 where a channel is formed is providedbetween two gate electrodes (the conductive layers 221 and 223). Whenthe transistor has the two gate electrodes, the threshold voltagethereof can be controlled. Alternatively, the two gate electrodes may beconnected to each other and supplied with the same signal to operate thetransistor. Such a transistor can have a higher field-effect mobilityand thus have a higher on-state current than other transistors.Consequently, a circuit capable of high-speed operation can be obtained.Furthermore, the area occupied by a circuit portion can be reduced. Theuse of the transistor having a high on-state current can reduce signaldelay in wirings and can reduce display unevenness even in a large-sizedor higher-resolution display device which has an increased number ofwirings.

Note that the transistor included in the circuit 34 and the transistorincluded in the display portion 32 may have the same structure. Aplurality of transistors included in the circuit 34 may have the samestructure or different structures. A plurality of transistors includedin the display portion 32 may have the same structure or differentstructures.

A material through which impurities such as water or hydrogen are noteasily diffused is preferably used for at least one of the insulatinglayers 212 and 213 covering the transistors. Such an insulating layercan serve as a harrier film. This structure can effectively prevent thediffusion of impurities into the transistors from the outside, and ahighly reliable display device be provided.

The conductive layer 224 over the insulating layer 214 serves as awiring. The conductive layer 224 is electrically connected to one of asource and a drain of any of the transistors through an opening providedin the insulating layers 214, 213, and 212. Furthermore, the conductivelayer 111 serving as a pixel electrode is provided over the insulatinglayer 215. The conductive layer 111 is electrically connected to any ofthe conductive layers 224 through an opening provided in the insulatinglayer 215. In FIG. 9, the conductive layer 111 is electrically connectedto one of the source and the drain of the transistor 205 through theconductive layer 224.

The insulating layer 216 is provided to cover an end portion of theconductive layer 111. The EL layer 112 is provided to cover the topsurfaces of the conductive layer 111, the insulating layer 216, and thestructure body 11. The conductive layer 113 is provided to cover the ELlayer 112.

In the light-emitting element 40, a material reflecting visible light isused for the conductive layer 111 and a material transmitting visiblelight is used for the conductive layer 113. With such a structure, atop-emission light-emitting element in which light is emitted to thesubstrate 31 side can be provided. Components such as the transistorsand capacitors can be positioned under the top-emission light-emittingelement, leading to improved aperture ratio. Note that a materialtransmitting visible light may be used for both of the conductive layers111 and 113, in which case a dual-emission light-emitting elementemitting light to both of the substrate 31 side and the substrate 21side is obtained.

A light-emitting element exhibiting a white color can be preferably usedas the light-emitting element 40. Thus, the light-emitting elements 40do not need to be separately fabricated in sub-pixels corresponding todifferent colors; accordingly, a display device with an extremely highdefinition can be provided. In that case, when light from thelight-emitting element 40 passes through the coloring layer 131 a or thelike, light out of a specific wavelength range is absorbed by thecoloring layer 131 a or the like. Consequently, red light is extracted,for example.

Alternatively, the light-emitting element 40 may have a microcavitystructure by using a material reflecting visible light for theconductive layer 111, using a semi-transmissive or semi-reflectivematerial for the conductive layer 113, and providing an opticaladjustment layer transmitting visible light between the conductivelayers 111 and 113. In that case, the optical adjustment layerpreferably has a different thickness in each sub-pixel corresponding toa different color. A sub-pixel including the optical adjustment layermay be provided in combination with a sub-pixel including no opticaladjustment layer.

The light-blocking layer 132 is provided on the surface of the substrate31 that faces the substrate 21. The coloring layers 131 a and 131 b areprovided to cover end portions of the light-blocking layer 132 and anopening in the light-blocking layer 132. The coloring layer 131 a andthe like each overlap with the light-emitting element 40. Part of thelight-blocking layer 132 overlaps with the structure body 11.

The structure body 11 can be formed using an insulating or conductivematerial. For example, the structure body 11 may be formed using aninsulating material similar to that for the insulating layer 216. In thecase where a conductive material is used for the structure body 11, thestructure body 11 is brought into an electrically floating state orsupplied with the same potential as the conductive layer 113, so thatthe EL layer 112 over the structure body 11 can be prevented fromemitting light.

FIG. 9 illustrates an example in which a polarizing plate 130 isprovided on the surface of the substrate 31 that is opposite to thesurface facing the substrate 21. As the polarizing plate 130, acircularly polarizing plate is preferably used. As the circularlypolarizing plate, for example, a stack including a linear polarizingplate and a quarter-wave retardation plate can be used. This results insuppression of external light reflection on a reflective member (e.g.,the conductive layer 111) provided in the display portion 32.

FIG. 9 illustrates an example in which the light-emitting element 40 issealed with the adhesive layer 141. When the adhesive layer 141 isformed using a material with a higher refractive index than air, theefficiency of extraction of light emitted from the light-emittingelement 40 can be increased as compared to the case where a space ismade between the light-emitting element 40 and the substrate 31.

Note that the adhesive layer 141 may be arranged on the outer edge ofthe display portion 32, i.e., a so-called sealed hollow structure may beemployed. In that case, a space formed by the substrates 21 and 31 andthe adhesive layer 141 may be filled with air; preferably, filled withan inert gas such as a rare gas or a nitrogen gas. When the space in asteady state is under reduced pressure relative to the atmosphericpressure, the following phenomenon can be prevented: the space expandsdepending on the usage environment (e.g., pressure or temperature) andthus the substrate 31 or the substrate 21 expands. Meanwhile, when thespace is under positive pressure relative to the atmospheric pressure,impurities such as moisture can be prevented from being diffused fromthe substrate 31, the substrate 21, the adhesive layer 141, or a gaptherebetween into the space.

The terminal portion 204 is provided in a region near an end portion ofthe substrate 21. The terminal portion 204 is electrically connected tothe FPC 42 through a connection layer 242. In the structure in FIG. 9,the terminal portion 204 is formed by stacking part of the wiring 35 andthe conductive layer 111.

The above is the description of Cross-sectional structure example 2-1.

Cross-Sectional Structure Example 2-2

FIG. 10 illustrates a cross-sectional structure example of the displaydevice 10 in which a substrate 171 and a substrate 181 havingflexibility are used as a pair of substrates. Part of a display surfaceof the display device 10 in FIG. 10 is bendable.

In the display device 10 illustrated in FIG. 10, the substrate 171, anadhesive layer 172, and an insulating layer 173 are provided instead ofthe substrate 21 in FIG. 9. Furthermore, the substrate 181, an adhesivelayer 182, and an insulating layer 183 are provided instead of thesubstrate 31.

The insulating layers 173 and 183 are preferably formed using a materialthrough which impurities such as water are not easily diffused.

The display device 10 in FIG. 10 has a structure in which eachtransistor and the light-emitting element 40 are sandwiched between theinsulating layers 173 and 183. Thus, even in the case where thesubstrate 171, the substrate 181, the adhesive layer 172, the adhesivelayer 182, or the like is formed using a material through whichimpurities such as water or hydrogen are easily diffused, the insulatinglayers 173 and 183 positioned further inward (closer to each transistoror the light-emitting element 40) than these components can suppressimpurity diffusion, so that reliability can be increased. In addition, avariety of materials can be used because there is no need to considerthe diffusion properties of impurities in the selection of materials forthe substrates 171 and 181, the adhesive layers 172 and 182, and thelike.

Example of Manufacturing Method

Here, a method for manufacturing a flexible display device is described.

For convenience, a layered structure including a pixel and a circuit, alayered structure including an optical member such as a coloring layer(color filter), a layered structure including an electrode or a wiringof a touch sensor, or the like is referred to as an element layer. Theelement layer includes, for example, a display element, and mayadditionally include a wiring electrically connected to the displayelement or an element such as a transistor used in a pixel or a circuit.

Here, a substrate refers to a member that supports an element layer inthe end and has flexibility (e.g., the substrate 171 or the substrate181 in FIG. 10). For example, an extremely thin (10 nm to 200 μm) filmis also referred to a substrate.

As a method for forming an element layer over a flexible substrateprovided with an insulating surface, the following two methods can betypically used: a method in which an element layer is formed directlyover a substrate; and a method in which an element layer is formed overa support substrate that is different from the substrate and then theelement layer is separated from the support substrate and transferred tothe substrate.

In the case where a material of the substrate can withstand heatingtemperature in a process for forming the element layer, it is preferablethat the element layer be formed directly over the substrate, in whichcase a manufacturing process can be simplified. At this time, theelement layer is preferably formed in a state where the substrate isfixed to a supporting base material, in which case transfer thereof inan apparatus and between apparatuses can be easy.

In the case of employing the method in which the element layer is formedover the supporting base material and then transferred to the substrate,first, a separation layer and an insulating layer are stacked over thesupporting base material, and then the element layer is formed over theinsulating layer. Next, the element layer is separated from thesupporting base material and then transferred to the substrate. At thistime, selected is a material with which separation at an interfacebetween the supporting base material and the separation layer, at aninterface between the separation layer and the insulating layer, or inthe separation layer occurs. In this method, a high heat-resistantmaterial is preferably used for the supporting base material and theseparation layer, because the upper temperature limit in manufacturingthe element layer can be increased to improve reliability.

For example, it is preferable that a stacked layer of a layer includinga high-melting-point metal material, such as tungsten, and a layerincluding an oxide of the metal material be used as the separationlayer, and a stacked layer of a plurality of layers, such as a siliconnitride layer, a silicon oxynitride layer, and a silicon nitride oxidelayer be used as the insulating layer over the separation layer. Notethat in this specification, oxynitride contains more oxygen thannitrogen, and nitride oxide contains more nitrogen than oxygen.

The element layer and the supporting base material can be separated byapplying mechanical power, by etching the separation layer, by injectinga liquid into the separation interface, or the like. Alternatively,separation may be performed by heating or cooling two layers of theseparation interface by utilizing a difference in thermal expansioncoefficient.

The separation layer is not necessarily provided in the case whereseparation can occur at an interface between the supporting basematerial and the insulating layer.

For example, glass and an organic resin such as polyimide can be used asthe supporting base material and the insulating layer, respectively. Inthat case, a separation trigger may be formed by, for example, locallyheating part of the organic resin with laser light or the like, or byphysically cutting part of or making a hole through the organic resinwith a sharp tool, so that separation may be performed at an interfacebetween the glass and the organic resin.

Alternatively, a heat-generation layer may be provided between thesupporting base material and the insulating layer formed of an organicresin, and separation may be performed at the interface between theheat-generation layer and the insulating layer by heating theheat-generation layer. The heat-generation layer can be formed using avariety of materials such as a material that generates heat when currentflows therethrough, a material that generates heat when absorbs light,or a material that generates heat when applied with a magnetic field.For example, a semiconductor, a metal, or an insulator can be selectedfor the heat-generation layer.

In the aforementioned methods, the insulating layer formed of an organicresin can be used as a substrate after the separation.

In the structure illustrated in FIG. 10, for example, a first separationlayer and the insulating layer 173 are formed in this order over a firstsupporting base material, and then components in a layer thereover areformed. Separately, a second separation layer and the insulating layer183 are formed in this order over a second supporting base material, andthen components in a layer thereover are formed. Next, the firstsupporting base material and the second supporting base material areattached to each other with the adhesive layer 141. After that,separation at an interface between the second separation layer and theinsulating layer 183 is conducted so that the second supporting basematerial and the second separation layer are removed, and then theinsulating layer 183 is attached to the substrate 181 with the adhesivelayer 182. Further, separation at an interface between the firstseparation layer and the insulating layer 173 is conducted so that thefirst supporting base material and the first separation layer areremoved, and then the substrate 171 is attached to the insulating layer173 with the adhesive layer 172. Note that either side may be subjectedto separation and attachment first.

The above is the description of a manufacturing method of a flexibledisplay device.

Components

The above components will be described below.

A material having a flat surface can be used as the substrate includedin the display device. The substrate on the side from which light fromthe display element is extracted is formed using a material transmittingthe light. For example, a material such as glass, quartz, ceramics,sapphire, or an organic resin can be used.

The weight and thickness of the display device can be reduced by using athin substrate. A flexible display device can be obtained by using asubstrate that is thin enough to have flexibility.

Since the substrate through which light emission is not extracted doesnot need to have a light-transmitting property, a metal substrate or thelike can be used in addition to the above-mentioned substrates. A metalmaterial, which has high thermal conductivity, is preferable because itcan easily conduct heat to the whole substrate and accordingly canprevent a local temperature rise in the display device. To obtainflexibility and bendability, the thickness of a metal substrate ispreferably greater than or equal to 10 μm and less than or equal to 200μm, more preferably greater than or equal to 20 μm and less than orequal to 50 μm.

Although there is no particular limitation on a material of a metalsubstrate, it is favorable to use, for example, a metal such asaluminum, copper, or nickel, an aluminum alloy, or an alloy such asstainless steel.

It is also possible to use a substrate subjected to insulationtreatment, e.g., a metal substrate whose surface is oxidized or providedwith an insulating film. The insulating film may be formed by, forexample, a coating method such as a spin-coating method or a dippingmethod, an electrodeposition method, an evaporation method, or asputtering method. An oxide film may be formed on the substrate surfaceby exposure to or heating in an oxygen atmosphere, an anodic oxidationmethod, or the like.

Examples of the material that has flexibility and transmits visiblelight include glass that is thin enough to have flexibility, polyesterresins such as polyethylene terephthalate (PET) and polyethylenenaphthalate (PEN), a polyacrylonitrile resin, a polyimide resin, apolymethyl methacrylate resin, a polycarbonate (PC) resin, apolyethersulfone (PES) resin, a polyamide resin, a cycloolefin resin, apolystyrene resin, a polyamide imide resin, a polyvinyl chloride resin,and a polytetrafluoroethylene (PTFE) resin. It is particularlypreferable to use a material with a low thermal expansion coefficient,for example, a material with a thermal expansion coefficient lower thanor equal to 30×10⁻⁶ /K, such as a polyamide imide resin, a polyimideresin, or PET. A substrate in which a glass fiber is impregnated with anorganic resin or a substrate whose thermal expansion coefficient isreduced by mixing an inorganic filler with an organic resin can also beused_(—) A substrate using such a material is lightweight, and thus adisplay device using this substrate can also be lightweight.

In the case where a fibrous body is included in the above material, ahigh-strength fiber of an organic compound or an inorganic compound isused as the fibrous body. The high-strength fiber is specifically afiber with a high tensile elastic modulus or a fiber with a high Young'smodulus. Typical examples thereof include a polyvinyl alcohol basedfiber, a polyester based fiber, a polyamide based fiber, a polyethylenebased fiber, an aramid based fiber, a polyparaphenylene benzobisoxazolefiber, a glass fiber, and a carbon fiber. As the glass fiber, glassfiber using E glass, S glass, D glass, Q glass, or the like can be used.These fibers may be used in a state of a woven or nonwoven fabric, and astructure body in which this fibrous body is impregnated with a resinand the resin is cured may be used as the flexible substrate. Thestructure body including the fibrous body and the resin is preferablyused as the flexible substrate, in which case the reliability againstbending or breaking due to local pressure can be increased.

Alternatively, glass, metal, or the like that is thin enough to haveflexibility can be used as the substrate. Alternatively, a compositematerial where glass and a resin material are bonded with an adhesivelayer may be used.

A hard coat layer (e.g., a silicon nitride layer or an aluminum oxidelayer) by which a touch panel surface is protected from damage, a layer(e.g., an aramid resin layer) that can disperse pressure, or the likemay be stacked over the flexible substrate. Furthermore, to suppress adecrease in the lifetime of the display element due to moisture and thelike, an insulating film with low water permeability may be stacked overthe flexible substrate. For example, an inorganic insulating materialsuch as silicon nitride, silicon oxynitride, silicon nitride oxide,aluminum oxide, or aluminum nitride can be used.

The substrate may be formed by stacking a plurality of layers.Particularly when a glass layer is used, a barrier property againstwater and oxygen can be improved and thus a highly reliable displaydevice can be provided.

Transistor

The transistor includes a conductive layer serving as the gateelectrode, the semiconductor layer, a conductive layer serving as thesource electrode, a conductive layer serving as the drain electrode, andan insulating layer serving as the gate insulating layer. In the above,a bottom-gate transistor is used.

Note that there is no particular limitation on the structure of thetransistor included in the touch panel of one embodiment of the presentinvention. For example, a planar transistor, a staggered transistor, oran inverted staggered transistor may be used. A top-gate transistor or abottom-gate transistor may be used. Gate electrodes may be providedabove and below a channel.

There is no particular limitation on the crystallinity of asemiconductor material used for the transistors, and an amorphoussemiconductor or a semiconductor having crystallinity (amicrocrystalline semiconductor, a polycrystalline semiconductor, asingle crystal semiconductor, or a semiconductor partly includingcrystal regions) may be used. It is preferable that a semiconductorhaving crystallinity be used, in which case deterioration of thetransistor characteristics can be suppressed.

As a semiconductor material used for the transistor, for example, anelement of Group 14 (e.g., silicon or germanium), a compoundsemiconductor, or an oxide semiconductor can be used. Typically, asemiconductor containing silicon, a semiconductor containing galliumarsenide, an oxide semiconductor containing indium, or the like can beused.

In particular, an oxide semiconductor having a wider band gap thansilicon is preferably used. A semiconductor material having a wider bandgap and a lower carrier density than silicon is preferably used becausethe off-state leakage current of the transistor can be reduced.

For the semiconductor layer, it is particularly preferable to use anoxide semiconductor including a plurality of crystal parts whose c-axesare aligned substantially perpendicular to a surface on which thesemiconductor layer is formed or the top surface of the semiconductorlayer and in which a grain boundary is not observed between adjacentcrystal parts.

There is no grain boundary in such an oxide semiconductor; therefore,generation of a crack in an oxide semiconductor film which is caused bystress when a display panel is bent is prevented. Therefore, such anoxide semiconductor can be preferably used for a flexible touch panelwhich is used in a bent state, or the like.

Moreover, the use of such an oxide semiconductor with crystallinity forthe semiconductor layer makes it possible to provide a highly reliabletransistor with a small change in electrical characteristics.

A transistor with an oxide semiconductor whose band gap is larger thanthe band gap of silicon has a low off-state current and therefore canhold charges stored in a capacitor that is series-connected to thetransistor for a long time. When such a transistor is used for a pixel,operation of a driver circuit can be stopped while a gray scale of eachpixel is maintained. As a result, a display device with extremely lowpower consumption can be obtained.

The semiconductor layer preferably includes, for example, a filmrepresented by an In-M-Zn-based oxide that contains at least indium,zinc, and M (a metal such as aluminum, titanium, gallium, germanium,yttrium, zirconium, lanthanum, cerium, tin, neodymium, or hafnium). Inorder to reduce variations in electrical characteristics of thetransistor including the oxide semiconductor, the oxide semiconductorpreferably contains a stabilizer in addition to indium, zinc, and M.

Examples of the stabilizer, including metals that can be used as M, aregallium, tin, hafnium, aluminum, and zirconium. As another stabilizer,lanthanoid such as lanthanum, cerium, praseodymium, neodymium, samarium,europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium,ytterbium, or lutetium can be given.

As an oxide semiconductor included in the semiconductor layer, any ofthe following can be used, for example: an In—Ga—Zn-based oxide, anIn—Al—Zn-based oxide, an In—Sn—Zn-based oxide, an In—Hf—Zn-based oxide,an In—La—Zn-based oxide, an In—Ce—Zn-based oxide, an In—Pr—Zn-basedoxide, an In—Nd—Zn-based oxide, an In—Sm—Zn-based oxide, anIn—Eu—Zn-based oxide, an In-Gd-Zn-based oxide, an In—Tb—Zn-based oxide,an In—Dy—Zn-based oxide, an In—Ho—Zn-based oxide, an In—Er—Zn-basedoxide, an In—Tm—Zn-based oxide, an In—Yb—Zn-based oxide, anIn—Lu—Zn-based oxide, an In—Sn—Ga—Zn-based oxide, an In—Hf—Ga—Zn-basedoxide, an In—Al—Ga—Zn-based oxide, an In—Sn—Al—Zn-based oxide, anIn—Sn—Hf—Zn-based oxide, and an In—Hf—Al—Zn-based oxide.

Note that here, an “In—Ga—Zn-based oxide” means an oxide containing In,Ga, and Zn as its main components, and there is no limitation on theratio of In:Ga:Zn. The In—Ga—Zn-based oxide may contain another metalelement in addition to In, Ga, and Zn.

The semiconductor layer and the conductive layer may include the samemetal elements contained in the above oxides. The use of the same metalelements for the semiconductor layer and the conductive layer can reducethe manufacturing cost. For example, when metal oxide targets with thesame metal composition are used, the manufacturing cost can be reduced,and the same etching gas or the same etchant can be used in processingthe semiconductor layer and the conductive layer. Note that even whenthe semiconductor layer and the conductive layer include the same metalelements, they have different compositions in some cases. For example, ametal element in a film is released during the manufacturing process ofthe transistor and the capacitor, which might vary the metalcompositions.

The energy gap of the oxide semiconductor included in the semiconductorlayer is 2 eV or more, preferably 2.5 eV or more, and more preferably 3eV or more. With the use of the oxide semiconductor having such a wideenergy gap, the off-state current of the transistor can be reduced.

In the case where the oxide semiconductor included in the semiconductorlayer is an In—M—Zn oxide, it is preferable that the atomic ratio ofmetal elements of a sputtering target used for forming a film of theIn—M—Zn oxide satisfy In≥M and Zn≥M. As the atomic ratio of metalelements of such a sputtering target, In:M:Zn=1:1:1, In:Al:Zn=1:1:1.2,In:M:Zn=3:1:2, In:M:Zn=4:2:4.1, and the like are preferable. Note thatthe atomic ratio of metal elements in the formed semiconductor layervaries from the above atomic ratio of metal elements of the sputteringtarget within a range of ±40% as an error.

An oxide semiconductor film with a low carrier density is used as thesemiconductor layer. For example, the semiconductor layer is an oxidesemiconductor film whose carrier density is lower than or equal to1×10¹⁷/cm³, preferably lower than or equal to 1×10¹⁵/cm³, morepreferably lower than or equal to 1×10¹³/cm³, still more preferablylower than or equal to 1×10¹¹/cm³, even more preferably lower than1×10¹⁰/cm³, and higher than or equal to 1×10⁻⁹/cm³. Such an oxidesemiconductor is referred to as a highly purified intrinsic orsubstantially highly purified intrinsic oxide semiconductor. The oxidesemiconductor has a low impurity concentration and a low density ofdefect states and can thus be referred to as an oxide semiconductorhaving stable characteristics.

Note that, without limitation to those described above, a material withan appropriate composition may be used depending on requiredsemiconductor characteristics and electrical characteristics (e.g.,field-effect mobility and threshold voltage) of a transistor. To obtainthe required semiconductor characteristics of the transistor, it ispreferable that the carrier density, the impurity concentration, thedefect density, the atomic ratio between a metal element and oxygen, theinteratomic distance, the density, and the like of the semiconductorlayer be set to appropriate values.

When silicon or carbon that is one of elements belonging to Group 14 iscontained in the oxide semiconductor included in the semiconductorlayer, the semiconductor layer includes an increased number of oxygenvacancies, and thus becomes n-type. Hence, the concentration of siliconor carbon (measured by secondary ion mass spectrometry) in thesemiconductor layer is lower than or equal to 2×10¹⁸ atoms/cm³,preferably lower than or equal to 2×10¹⁷ atoms/cm³;

Alkali metal and alkaline earth metal might generate carriers whenbonded to an oxide semiconductor, in which case the off-state current ofthe transistor might be increased. Therefore, the concentration ofalkali metal or alkaline earth metal of the semiconductor layer, whichis measured by secondary ion mass spectrometry, is lower than or equalto 1×10¹⁸ atoms/cm³, preferably lower than or equal to 2×10¹⁶ atoms/cm³.

When nitrogen is contained in the oxide semiconductor included in thesemiconductor layer, electrons serving as carriers are generated and thecarrier density increases, so that the semiconductor layer easilybecomes n-type. Thus, a transistor including an oxide semiconductorwhich contains nitrogen is likely to be normally on. Hence, theconcentration of nitrogen which is measured by secondary ion massspectrometry is preferably set to lower than or equal to 5×10¹⁸atoms/cm³.

The semiconductor layer may have a non-single-crystal structure, forexample. The non-single-crystal structure includes, for example, CAAC-OS(c-axis aligned crystalline oxide semiconductor, or c-axis aligned anda-b-plane-anchored crystalline oxide semiconductor), a polycrystallinestructure, a microcrystalline structure, or an amorphous structure.Among the non-single-crystal structures, an amorphous structure has thehighest density of defect states, whereas CAAC-OS has the lowest densityof defect states.

An oxide semiconductor film having an amorphous structure has, forexample, disordered atomic arrangement and no crystalline component.Alternatively, an oxide film having an amorphous structure has, forexample, an absolutely amorphous structure and no crystal part.

Note that the semiconductor layer may be a mixed film including two ormore of the following: a region having an amorphous structure, a regionhaving a microcrystalline structure, a region having a polycrystallinestructure, a region of CAAC-OS, and a region having a single crystalstructure. The mixed film has, for example, a single-layer structure ora stacked-layer structure including two or more of the above regions insome cases.

<Composition of CAC-OS>

Described below is the composition of a cloud aligned complementaryoxide semiconductor (CAC-OS) applicable to a transistor disclosed in oneembodiment of the present invention.

In this specification and the like, a metal oxide means an oxide ofmetal in a broad sense. Metal oxides are classified into an oxideinsulator, an oxide conductor (including a transparent oxide conductor),an oxide semiconductor (also simply referred to as an OS), and the like.For example, a metal oxide used in an active layer of a transistor iscalled an oxide semiconductor in some cases. In other words, an OS FETis a transistor including a metal oxide or an oxide semiconductor.

In this specification, a metal oxide in which regions functioning as aconductor and regions functioning as a dielectric are mixed and whichfunctions as a semiconductor as a whole is defined as a CAC-OS or aCAC-metal oxide.

The CAC-OS has, for example, a composition in which elements included inan oxide semiconductor are unevenly distributed. Materials includingunevenly distributed elements each have a size of greater than or equalto 0.5 nm and less than or equal to 10 nm, preferably greater than orequal to 0.5 nm and less than or equal to 3 nm, or a similar size. Notethat in the following description of an oxide semiconductor, a state inwhich one or more elements are unevenly distributed and regionsincluding the element(s) are mixed is referred to as a mosaic pattern ora patch-like pattern. The region has a size of greater than or equal to0.5 nm and less than or equal to 10 nm, preferably greater than or equalto 0.5 nm and less than or equal to 3 nm, or a similar size.

The physical properties of a region including an unevenly distributedelement are determined by the properties of the element. For example, aregion including an unevenly distributed element which relatively tendsto serve as an insulator among elements included in a metal oxide servesas a dielectric region. in contrast, a region including an unevenlydistributed element which relatively tends to serve as a conductor amongelements included in a metal oxide serves as a conductive region. Amaterial in which conductive regions and dielectric regions are mixed toform a mosaic pattern serves as a semiconductor.

That is, a metal oxide in one embodiment of the present invention is akind of matrix composite or metal matrix composite, in which materialshaving different physical properties are mixed.

Note that an oxide semiconductor preferably contains at least indium. Inparticular, indium and zinc are preferably contained. In addition, anelement Al (Al is one or more of gallium, aluminum, silicon, boron,yttrium, copper, vanadium, beryllium, titanium, iron, nickel, germanium,zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum,tungsten, magnesium, and the like) may be contained.

For example, of the CAC-OS, an In—Ga—Zn oxide with the CAC composition(such an In—Ga—Zn oxide may be particularly referred to as CAC-IGZO) hasa composition in which materials are separated into indium oxide(InO_(X1), where X1 is a real number greater than 0) or indium zincoxide (In_(X2)Zn_(Y2)O_(Z2), where X2, Y2, and Z2 are real numbersgreater than 0), and gallium oxide (GaO_(X3), where X3 is a real numbergreater than 0), gallium zinc oxide (Ga_(X4)Zn_(Y4)O_(Z4), where X4, Y4,and Z4 are real numbers greater than 0), or the like, and a mosaicpattern is formed. Then, InO_(X1) and In_(X2)Zn_(Y2)O_(Z2) forming themosaic pattern are evenly distributed in the film. This composition isalso referred to as a cloud-like composition.

That is, the CAC-OS is a composite oxide semiconductor with acomposition in which a region including GaO_(X3) as a main component anda region including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main componentare mixed. Note that in this specification, for example, when the atomicratio of In to an element M in a first region is greater than the atomicratio of In to an element M in a second region, the first region hashigher In concentration than the second region.

Note that a compound including In, Ga, Zn, and O is also known as IGZO.Typical examples of IGZO include a crystalline compound represented byInGaO₃(ZnO)_(m1)(m1 is a natural number) and a crystalline compoundrepresented by In_((1-x0))O₃(ZnO)_(m0)(−1≤x0≤1; m0 is a given number).

The above crystalline compounds have a single crystal structure, apolycrystalline structure, or a CAAC structure. Note that the CAACstructure is a crystal structure in which a plurality of IGZOnanoctystals have c-axis alignment and are connected in the a-b planedirection without alignment.

On the other hand, the CAC-OS relates to the material composition of anoxide semiconductor. In a material composition of a CAC-OS including In,Ga, Zn, and O, nanoparticle regions including Ga as a main component areobserved in part of the CAC-OS and nanoparticle regions including In asa main component are observed in part thereof. These nanoparticleregions are randomly dispersed to form a mosaic pattern. Therefore, thecrystal structure is a secondary element for the CAC-OS.

Note that in the CAC-OS, a stacked-layer structure including two or morefilms with different atomic ratios is not included. For example, atwo-layer structure of a film including In as a main component and afilm including Ga as a main component is not included.

A boundary between the region including GaO_(X3) as a main component andthe region including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a maincomponent is not clearly observed in some cases.

In the case where one or more of aluminum, silicon, boron, yttrium,copper, vanadium, beryllium, titanium, iron, nickel, germanium,zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum,tungsten, magnesium, and the like are contained instead of gallium in aCAC-OS, nanoparticle regions including the selected element(s) as a maincomponent(s) are observed in part of the CAC-OS and nanoparticle regionsincluding In as a main component are observed in part thereof, and thesenanoparticle regions are randomly dispersed to form a mosaic pattern inthe CAC-OS.

<Analysis of CAC-OS>

Next, measurement results of an oxide semiconductor over a substrate bya variety of methods are described.

«Structure of Samples and Formation Method Thereof»

Nine samples of one embodiment of the present invention arc describedbelow. The samples are formed at different substrate temperatures andwith different ratios of an oxygen gas flow rate in formation of theoxide semiconductor. Note that each sample includes a substrate and anoxide semiconductor over the substrate.

A method for forming the samples is described.

A glass substrate is used as the substrate. Over the glass substrate, a100-nm-thick In—Ga—Zn oxide is formed as an oxide semiconductor with asputtering apparatus. The formation conditions are as follows: thepressure in a chamber is 0.6 Pa, and an oxide target (with an atomicratio of In:Ga:Zn=4:2:4.1) is used as a target. The oxide targetprovided in the sputtering apparatus is supplied with an AC power of2500 W.

As for the conditions in the formation of the oxide of the nine samples,the substrate temperature is set to a temperature that is not increasedby intentional heating (hereinafter such a temperature is also referredto as room temperature or R.T.), to 130° C., and to 170° C. The ratio ofa flow rate of an oxygen gas to a flow rate of a mixed gas of Ar andoxygen (also referred to as an oxygen gas flow rate ratio) is set to10%, 30%, and 100%.

«Analysis By X-ray Diffraction»

In this section, results of X-ray diffraction (XRD) measurementperformed on the nine samples are described. As an XRD apparatus, D8ADVANCE manufactured by Bruker AXS is used. The conditions are asfollows: scanning is performed by an out-of-plane method at one, thescanning range is 15 deg. to 50 deg., the step width is 0.02 deg., andthe scanning speed is 3.0 deg./min.

FIG. 30 shows XRD spectra measured by an out-of-plane method. In FIG.30, the top row shows the measurement results of the samples formed at asubstrate temperature of 170° C.; the middle row shows the measurementresults of the samples formed at a substrate temperature of 130° C.; andthe bottom row shows the measurement results of the samples formed at asubstrate temperature of R.T. The left column shows the measurementresults of the samples formed with an oxygen gas flow rate ratio of 10%;the middle column shows the measurement results of the samples formedwith an oxygen gas flow rate ratio of 30%; and the right column showsthe measurement results of the samples formed with an oxygen gas flowrate ratio of 100%.

In the XRD spectra shown in FIG. 30, the higher the substratetemperature at the time of formation is or the higher the oxygen gasflow rate ratio at the time of formation is, the higher the intensity ofthe peak at around 2θ=31° is. Note that it is found that the peak ataround 2θ=31° is derived from a crystalline IGZO compound whose c-axesare aligned in a direction substantially perpendicular to a formationsurface or a top surface of the crystalline IGZO compound (such acompound is also referred to as c-axis aligned crystalline (CAAC) IGZO).

As shown in the XRD spectra in FIG. 30, as the substrate temperature atthe time of formation is lower or the oxygen gas flow rate ratio at thetime of formation is lower, a peak becomes less clear. Accordingly, itis found that there are no alignment in the a-b plane direction andc-axis alignment in the measured areas of the samples that are formed ata lower substrate temperature or with a lower oxygen gas flow rateratio.

«Analysis With Electron Microscope»

This section describes the observation and analysis results of thesamples formed at a substrate temperature of R.T. and with an oxygen gasflow rate ratio of 10% with a high-angle annular dark-field scanningtransmission electron microscope (HAADF-STEM). An image obtained with anHAADF-STEM is also referred to as a TEM image.

Described are the results of image analysis of plan-view images andcross-sectional images obtained with an HAADF-STEM (also referred to asplan-view TEM images and cross-sectional TEM images, respectively). TheTEM images are observed with a spherical aberration corrector function.The HAADF-STEM images are obtained using an atomic resolution analyticalelectron microscope JEM-ARM200F manufactured by JEOL Ltd. under thefollowing conditions: the acceleration voltage is 200 kV, andirradiation with an electron beam with a diameter of approximately 0.1nm is performed.

FIG. 31A is a plan-view TEM image of the sample formed at a substratetemperature of R.T. and with an oxygen gas flow rate ratio of 10%. FIG.31B is a cross-sectional TEM image of the sample formed at a substratetemperature of R.T. and with an oxygen gas flow rate ratio of 10%.

«Analysis of Electron Diffraction Patterns»

This section describes electron diffraction patterns obtained byirradiation of the sample formed at a substrate temperature of R.T. andan oxygen gas flow rate ratio of 10% with an electron beam with a probediameter of 1 nm (also referred to as a nanobeam).

Electron diffraction patterns of points indicated by black dots a1, a2,a3, a4, and a5 in the plan-view TEM image in FIG. 31A of the sampleformed at a substrate temperature of R.T. and an oxygen gas flow rateratio of 10% are observed. Note that the electron diffraction patternsare observed while electron beam irradiation is performed at a constantrate for 35 seconds. FIGS. 31C, 31D, 31E, 31F, and 31G show the resultsof the points indicated by the black dots a1, a2, a3, a4, and a5,respectively.

In FIGS. 31C, 31D, 31E, 31F, and 31G, regions with high luminance in acircular (ring) pattern can be shown. Furthermore, a plurality of spotscan be shown in a ring-like shape.

Electron diffraction patterns of points indicated by black dots b1, b2,b3, b4, and b5 in the cross-sectional TEM image in FIG. 31B of thesample formed at a substrate temperature of R.T. and an oxygen gas flowrate ratio of 10% are observed. FIGS. 31H, 31I, 31J, 31K, and 31L showthe results of the points indicated by the black dots b11, b2, b3, b4,and b5, respectively.

In FIGS. 31H, 31I, 31J, 31K, and 31L, regions with high luminance in aring pattern can be shown. Furthermore, a plurality of spots can beshown in a ring-like shape.

For example, when an electron beam with a probe diameter of 300 nm isincident on a CAAC-OS including an InGaZnO₄ crystal in a directionparallel to the sample surface, a diffraction pattern including a spotderived from the (009) plane of the InGaZnO₄ crystal is obtained. Thatis, the CAAC-OS has c-axis alignment and the c-axes are aligned in thedirection substantially perpendicular to the formation surface or thetop surface of the CAAC-OS. Meanwhile, a ring-like diffraction patternis shown when an electron beam with a probe diameter of 300 nm isincident on the same sample in a direction perpendicular to the samplesurface. That is, it is found that the CAAC-OS has neither a-axisalignment nor b-axis alignment.

Furthermore, a diffraction pattern like a halo pattern is observed whenan oxide semiconductor including a nanocrystal (a nanocrystalline oxidesemiconductor (nc-OS)) is subjected to electron diffraction using anelectron beam with a large probe diameter (e.g., 50 nm or larger).Meanwhile, bright spots are shown in a nanobeam electron diffractionpattern of the nc-OS obtained using an electron beam with a small probediameter (e.g., smaller than 50 nm). Furthermore, in a nanobeam electrondiffraction pattern of the nc-OS, regions with high luminance in acircular (ring) pattern are shown in some cases. Also in a nanobeamelectron diffraction pattern of the nc-OS, a plurality of bright spotsare shown in a ring-like shape in some cases.

The electron diffraction pattern of the sample formed at a substratetemperature of R.T. and with an oxygen gas flow rate ratio of 10% hasregions with high luminance in a ring pattern and a plurality of brightspots appear in the ring-like pattern. Accordingly, the sample formed ata substrate temperature of R.T. and with an oxygen gas flow rate ratioof 10% exhibits an electron diffraction pattern similar to that of thenc-OS and does not show alignment in the plane direction and thecross-sectional direction.

According to what is described above, an oxide semiconductor formed at alow substrate temperature or with a low oxygen gas flow rate ratio islikely to have characteristics distinctly different from those of anoxide semiconductor film having an amorphous structure and an oxidesemiconductor film having a single crystal structure.

«Elementary Analysis»

This section describes the analysis results of elements included in thesample formed at a substrate temperature of R.T. and with an oxygen gasflow rate ratio of 10%. For the analysis, by energy dispersive X-rayspectroscopy (EDX), EDX mapping images are obtained. An energydispersive X-ray spectrometer AnalysisStation JED-2300T manufactured byJEOL Ltd. is used as an elementary analysis apparatus in the EDXmeasurement. A Si drift detector is used to detect an X-ray emitted fromthe sample.

In the EDX measurement, an EDX spectrum of a point is obtained in such amanner that electron beam irradiation is performed on the point in adetection target region of a sample, and the energy of characteristicX-ray of the sample generated by the irradiation and its frequency aremeasured. In this embodiment, peaks of an EDX spectrum of the point areattributed to electron transition to the L shell in an In atom, electrontransition to the K shell in a Ga atom, and electron transition to the Kshell in a Zn atom and the K shell in an O atom, and the proportions ofthe atoms in the point are calculated. An EDX mapping image indicatingdistributions of proportions of atoms can be obtained through theprocess in an analysis target region of a sample.

FIGS. 32A to 32C show EDX mapping images in a cross section of thesample formed at a substrate temperature of R.T. and with an oxygen gasflow rate ratio of 10%. FIG. 32A shows an EDX mapping image of Ga atoms.The proportion of the Ga atoms in all the atoms is 1.18 atomic % to18.64 atomic %. FIG. 32B shows an EDX mapping image of In atoms. Theproportion of the In atoms in all the atoms is 9.28 atomic % to 33.74atomic %. FIG. 32C shows an EDX mapping image of Zn atoms. Theproportion of the Zn atoms in all the atoms is 6.69 atomic % to 24.99atomic %. FIGS. 32A to 32C show the same region in the cross section ofthe sample formed at a substrate temperature of R.T. and with an oxygengas flow rate ratio of 10%. In the EDX mapping images, the proportion ofan element is indicated by grayscale: the more measured atoms exist in aregion, the brighter the region is; the less measured atoms exist in aregion, the darker the region is. The magnification of the EDX mappingimages in FIGS. 32A to 32C is 7200000 times.

The EDX mapping images in FIGS. 32A to 32C show relative distribution ofbrightness indicating that each element has a distribution in the sampleformed at a substrate temperature of R.T. and with an oxygen gas flowrate ratio of 10%. Areas surrounded by solid lines and areas surroundedby dashed lines in FIGS. 32A to 32C are examined.

In FIG. 32A, a relatively dark region occupies a large area in the areasurrounded by the solid line, while a relatively bright region occupiesa large area in the area surrounded by the dashed line. In FIG. 32B, arelatively bright region occupies a large area in the area surrounded bythe solid line, while a relatively dark region occupies a large area inthe area surrounded by the dashed line.

That is, the areas surrounded by the solid lines are regions including arelatively large number of In atoms and the areas surrounded by thedashed lines are regions including a relatively small number of Inatoms. In FIG. 32C, the right portion of the area surrounded by thesolid line is relatively bright and the left portion thereof isrelatively dark. Thus, the area surrounded by the solid line is a regionincluding In_(X2)Zn_(Y2)O_(Z2), InO_(X1), and the like as maincomponents.

The area surrounded by the solid line is a region including a relativelysmall number of Ga atoms and the area surrounded by the dashed line is aregion including a relatively large number of Ga atoms. In FIG. 32C, theupper left portion of the area surrounded by the dashed line isrelatively bright and the lower right portion thereof is relativelydark. Thus, the area surrounded by the dashed line is a region includingGaO_(X3), Ga_(Y4)Zn_(Y4)O_(Z4), and the like as main components.

Furthermore, as shown in FIGS. 32A to 32C, the In atoms are relativelymore uniformly distributed than the Ga atoms, and regions includingInO_(X1) as a main component is seemingly joined to each other through aregion including In_(X2)Zn_(Y2)O_(Z2) as a main component. Thus, theregions including In_(X2)Zn_(Y2)O_(Z2) and InO_(X1) as main componentsextend like a cloud.

An In—Ga—Zn oxide having a composition in which the regions includingGaO_(X3) or the like as a main component and the regions includingIn_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main component are unevenlydistributed and mixed can be referred to as a CAC-OS.

The crystal structure of the CAC-OS includes an nc structure. In anelectron diffraction pattern of the CAC-OS with the nc structure,several or more bright spots appear in addition to bright sports derivedfrom IGZO including a single crystal, a polycrystal, or a CAAC.Alternatively, the crystal structure is defined as having high luminanceregions appearing in a ring pattern in addition to the several or morebright spots.

As shown in FIGS. 32A to 32C, each of the regions including GaO_(X3) orthe like as a main component and the regions includingIn_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main component has a size ofgreater than or equal to 0.5 nm and less than or equal to 10 nm, orgreater than or equal to 1 nm and less than or equal to 3 nm. Note thatit is preferable that a diameter of a region including each metalelement as a main component be greater than or equal to 1 nm and lessthan or equal to 2 nm in the EDX mapping images.

As described above, the CAC-OS has a structure different from that of anIGZO compound in which metal elements are evenly distributed, and hascharacteristics different from those of the IGZO compound. That is, inthe CAC-OS, regions including GaO_(X3) or the like as a main componentand regions including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a maincomponent are separated to form a mosaic pattern.

The conductivity of a region including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1)as a main component is higher than that of a region including GaO_(X3)or the like as a main component. In other words, when carriers flowthrough regions including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a maincomponent, the conductivity of an oxide semiconductor exhibits.Accordingly, when regions including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) asa main component are distributed in an oxide semiconductor like a cloud,high field-effect mobility (μ) can be achieved.

In contrast, the insulating property of a region including GaO_(X3) orthe like as a main component is higher than that of a region includingIn_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main component. In other words,when regions including GaO_(X3) or the like as a main component aredistributed in an oxide semiconductor, leakage current can be suppressedand favorable switching operation can be achieved.

Accordingly, when a CAC-OS is used for a semiconductor element, theinsulating property derived from GaO_(X3) or the like and theconductivity derived from In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) complementeach other, whereby high on-state current (I_(on)) and high field-effectmobility (μ) can be achieved.

A semiconductor element including a CAC-OS has high reliability. Thus,the CAC-OS is suitably used in a variety of semiconductor devicestypified by a display.

Alternatively, silicon is preferably used as a semiconductor in which achannel of a transistor is formed. Although amorphous silicon may beused as silicon, silicon having crystallinity is particularlypreferable. For example, microcrystalline silicon, polycrystallinesilicon, single crystal silicon, or the like is preferably used. Inparticular, polycrystalline silicon can be formed at a lower temperaturethan single crystal silicon and has higher field effect mobility andhigher reliability than amorphous silicon. When such a polycrystallinesemiconductor is used for a pixel, the aperture ratio of the pixel canbe improved. Even in the case where pixels are provided at extremelyhigh resolution, a gate driver circuit and a source driver circuit canbe formed over a substrate over which the pixels are formed, and thenumber of components of an electronic device can be reduced.

The bottom-gate transistor described in this embodiment is preferablebecause the number of manufacturing steps can be reduced. When amorphoussilicon, which can be formed at a lower temperature than polycrystallinesilicon, is used for the semiconductor layer, materials with low heatresistance can be used for a wiring, an electrode, or a substrate belowthe semiconductor layer, resulting in wider choice of materials. Forexample, an extremely large glass substrate can be favorably used.Meanwhile, the top-gate transistor is preferable because an impurityregion is easily formed in a self-aligned manner and variation incharacteristics can be reduced. In that case, the use of polycrystallinesilicon, single crystal silicon, or the like is particularly preferable.

[Conductive Layer]

As materials for a gate, a source, and a drain of a transistor, and aconductive layer such as a wiring or an electrode included in a displaydevice, any of metals such as aluminum, titanium, chromium, nickel,copper, yttrium, zirconium, molybdenum, silver, tantalum, and tungsten,or an alloy containing any of these metals as its main component can beused. A single-layer structure or multi-layer structure including a filmcontaining any of these materials can be used. For example, thefollowing structures can be given: a single-layer structure of analuminum film containing silicon, a two-layer structure in which analuminum film is stacked over a titanium film, a two-layer structure inwhich an aluminum film is stacked over a tungsten film, a two-layerstructure in which a copper film is stacked over acopper-magnesium-aluminum alloy film, a two-layer structure in which acopper film is stacked over a titanium film, a two-layer structure inwhich a copper film is stacked over a tungsten film, a three-layerstructure in which a titanium film or a titanium nitride film, analuminum film or a copper film, and a titanium film or a titaniumnitride film are stacked in this order, and a three-layer structure inwhich a molybdenum film or a molybdenum nitride film, an aluminum filmor a copper film, and a molybdenum film or a molybdenum nitride film arestacked in this order. Note that an oxide such as indium oxide, tinoxide, or zinc oxide may be used. Copper containing manganese ispreferably used because the controllability of a shape by etching isincreased.

As a light-transmitting conductive material, a conductive oxide such asindium oxide, indium tin oxide, indium zinc oxide, zinc oxide, or zincoxide to which gallium is added, or graphene can be used. Alternatively,a metal material such as gold, silver, platinum, magnesium, nickel,tungsten, chromium, molybdenum, iron, cobalt, copper, palladium, ortitanium, or an alloy material containing any of these metal materialscan be used. Alternatively, a nitride of the metal material (e.g.,titanium nitride) or the like may be used. in the case of using themetal material or the alloy material (or the nitride thereof), thethickness is set small enough to be able to transmit light.Alternatively, a stack of any of the above materials can be used as theconductive layer. For example, a stacked film of indium tin oxide and analloy of silver and magnesium is preferably used because theconductivity can be increased. They can also be used for conductivelayers such as a variety of wirings and electrodes included in a displaydevice, and conductive layers (e.g., conductive layers serving as apixel electrode or a common electrode) included in a display element.

[Insulating Layer]

Examples of an insulating material that can be used for the insulatinglayers include a resin such as acrylic or epoxy resin, a resin having asiloxane bond, and an inorganic insulating material such as siliconoxide, silicon oxynitride, silicon nitride oxide, silicon nitride, oraluminum oxide.

The light-emitting element is preferably provided between a pair ofinsulating films with low water permeability, in which case impuritiessuch as water can be prevented from entering the light-emitting element,preventing a decrease in the reliability of the device.

As an insulating film with low water permeability, a film containingnitrogen and silicon (e.g., a silicon nitride film or a silicon nitrideoxide film), a film containing nitrogen and aluminum (e.g., an aluminumnitride film), or the like can be used. Alternatively, a silicon oxidefilm, a silicon oxynitride film, an aluminum oxide film, or the like maybe used.

For example, the water vapor transmittance of the insulating film withlow water permeability is lower than or equal to 1×10⁻⁵ [g/(m².day)],preferably lower than or equal to 1×10⁻⁶[g/(m².day)], further preferablylower than or equal to 1×10⁻⁷[g/(m².day)], and still further preferablylower than or equal to 1×10⁻⁸[g/(m².day)].

[Light-Emitting Element]

As the light-emitting element, a self-luminous element can be used, andan element whose luminance is controlled by current or voltage isincluded in the category of the light-emitting element. For example, alight-emitting diode (LED), an organic EL element, an inorganic ELelement, or the like can be used.

The light-emitting element may be a top emission, bottom emission, ordual emission light-emitting element. A conductive film that transmitsvisible light is used as the electrode through which light is extracted.A conductive film that reflects visible light is preferably used as theelectrode through which light is not extracted.

The EL layer includes at least a light-emitting layer. In addition tothe light-emitting layer, the EL layer may further include a layercontaining any of a substance with a high hole-injection property, asubstance with a high hole-transport property, a hole-blocking material,a substance with a high electron-transport property, a substance with ahigh electron-injection property, a substance with a bipolar property (asubstance with a high electron- and hole-transport property), and thelike.

Either a low molecular compound or a high molecular compound can be usedfor the EL layer, and an inorganic compound may also be included. Thelayers included in the EL layer can be formed by any of the followingmethods: an evaporation method (including a vacuum evaporation method),a transfer method, a printing method, an inkjet method, a coatingmethod, and the like.

When a voltage higher than the threshold voltage of the light-emittingelement is applied between the anode and the cathode, holes are injectedto the EL layer from the anode side and electrons are injected to the ELlayer from the cathode side. The injected electrons and holes arerecombined in the EL layer, so that a light-emitting substance containedin the EL layer emits light.

In the case where a light-emitting element emitting white light is usedas the light-emitting element, the EL layer preferably contains two ormore kinds of light-emitting substances. For example, light-emittingsubstances are selected so that two or more light-emitting substancesemit complementary colors to obtain white light emission. Specifically,it is preferable to contain two or more light-emitting substancesselected from light-emitting substances emitting light of red (R), green(G), blue (B), yellow (Y), orange (O), and the like and light-emittingsubstances emitting light containing two or more of spectral componentsof R, G, and B. The light-emitting element preferably emits light with aspectrum having two or more peaks in the wavelength range of a visiblelight region (e.g., 350 nm to 750 nm). An emission spectrum of amaterial emitting light having a peak in the wavelength range of ayellow light preferably includes spectral components also in thewavelength range of a green light and a red light.

A light-emitting layer containing a light-emitting material emittinglight of one color and a light-emitting layer containing alight-emitting material emitting light of another color are preferablystacked in the EL layer. For example, the plurality of light-emittinglayers in the EL layer may be stacked in contact with each other or maybe stacked with a region not including any light-emitting materialtherebetween. For example, between a fluorescent layer and aphosphorescent layer, a region containing the same material as one inthe fluorescent layer or phosphorescent layer (for example, a hostmaterial or an assist material) and no light-emitting material may beprovided. This facilitates the manufacture of the light-emitting elementand reduces the drive voltage.

The light-emitting element may be a single element including one ELlayer or a tandem element in which a plurality of EL layers are stackedwith a charge generation layer therebetween.

The conductive film that transmits visible light can be formed using,for example, indium oxide, indium tin oxide, indium zinc oxide, zincoxide, or zinc oxide to which gallium is added. Alternatively, a film ofa metal material such as gold, silver, platinum, magnesium, nickel,tungsten, chromium, molybdenum, iron, cobalt, copper, palladium, ortitanium; an alloy containing any of these metal materials; or a nitrideof any of these metal materials (e.g., titanium nitride) can be usedwhen formed thin so as to have a light-transmitting property.Alternatively, a stacked film of any of the above materials can be usedas the conductive layer. For example, a stacked film of indium tin oxideand an alloy of silver and magnesium is preferably used, in which caseconductivity can be increased. Further alternatively, graphene or thelike may be used.

For the conductive film that reflects visible light, for example, ametal material such as aluminum, gold, platinum, silver, nickel,tungsten, chromium, molybdenum, iron, cobalt, copper, or palladium, oran alloy including any of these metal materials can be used. Lanthanum,neodymium, germanium, or the like may be added to the metal material orthe alloy. Alternatively, an alloy containing aluminum (an aluminumalloy) such as an alloy of aluminum and titanium, an alloy of aluminumand nickel, or an alloy of aluminum and neodymium may be used.Alternatively, an alloy containing silver such as an alloy of silver andcopper, an alloy of silver and palladium, or an alloy of silver andmagnesium may be used. An alloy of silver and copper is preferablebecause of its high heat resistance. Furthermore, when a metal film or ametal oxide film is stacked in contact with an aluminum film or analuminum alloy film, oxidation can be suppressed. Examples of a materialfor the metal film or the metal oxide film include titanium and titaniumoxide. Alternatively, the conductive film having a property oftransmitting visible light and a film containing any of the above metalmaterials may be stacked. For example, a stack of silver and indium tinoxide, a stack of an alloy of silver and magnesium and indium tin oxide,or the like can be used.

The electrodes may each be formed by an evaporation method or asputtering method. Alternatively, a discharging method such as an inkjetmethod, a printing method such as a screen printing method, or a platingmethod may be used.

Note that the aforementioned light-emitting layer and layers containinga substance with a high hole-injection property, a substance with a highhole-transport property, a substance with a high electron-transportproperty, a substance with a high electron-injection property, and asubstance with a bipolar property may include an inorganic compound suchas a quantum dot or a high molecular compound (e.g., an oligomer, adendrimer, and a polymer). For example, used for the light-emittinglayer, the quantum dot can serve as a light-emitting material.

The quantum dot may be a colloidal quantum dot, an alloyed quantum dot,a core-shell quantum dot, a core quantum dot, or the like. The quantumdot containing elements belonging to Groups 12 and 16, elementsbelonging to Groups 13 and 15, or elements belonging to Groups 14 and16, may be used. Alternatively, the quantum dot containing an elementsuch as cadmium, selenium, zinc, sulfur, phosphorus, indium, tellurium,lead, gallium, arsenic, or aluminum may be used.

[Liquid Crystal Element]

The liquid crystal element can employ, for example, a vertical alignment(VA) mode. Examples of the vertical alignment mode include amulti-domain vertical alignment (MVA) mode, a patterned verticalalignment (PVA) mode, and an advanced super view (ASV) mode.

The liquid crystal element can employ a variety of modes; for example,other than the VA mode, a twisted nematic (TN) mode, an in-planeswitching (IPS) mode, a fringe field switching (FFS) mode, an axiallysymmetric aligned micro-cell (ASM) mode, an optically compensatedbirefringence (OCB) mode, a ferroelectric liquid crystal (FLC) mode, oran antiferroelectric liquid crystal (AFLC) mode can be used.

The liquid crystal element controls the transmission or non-transmissionof light utilizing an optical modulation action of a liquid crystal.Note that the optical modulation action of the liquid crystal iscontrolled by an electric field applied to the liquid crystal (includinga horizontal electric field, a vertical electric field, or an obliqueelectric field). As the liquid crystal used for the liquid crystalelement, thermotropic liquid crystal, low-molecular liquid crystal,high-molecular liquid crystal, polymer dispersed liquid crystal (PDLC),ferroelectric liquid crystal, anti-ferroelectric liquid crystal, or thelike can be used. These liquid crystal materials exhibit a cholestericphase, a smectic phase, a cubic phase, a chiral nematic phase, anisotropic phase, or the like depending on conditions.

As the liquid crystal material, either a positive liquid crystal or anegative liquid crystal may be used, and an appropriate liquid crystalmaterial can be used depending on the mode or design to be used.

An alignment film can be provided to adjust the alignment of a liquidcrystal. In the case where a horizontal electric field mode is employed,a liquid crystal exhibiting a blue phase for which an alignment film isunnecessary may be used. The blue phase is a liquid crystal phase, whichis generated just before a cholesteric phase changes into an isotropicphase when the temperature of a cholesteric liquid crystal is increased.Since the blue phase appears only in a narrow temperature range, aliquid crystal composition in which several weight percent or more of achiral material is mixed is used for the liquid crystal layer in orderto improve the temperature range. The liquid crystal compositioncontaining a liquid crystal exhibiting a blue phase and a chiralmaterial has a short response time and optical isotropy, whicheliminates the need for an alignment process and reduces the viewingangle dependence. Since the alignment film does not need to be provided,rubbing treatment is not necessary; accordingly, electrostatic dischargedamage caused by the rubbing treatment can be prevented, reducingdefects and damage of a liquid crystal display device in themanufacturing process.

The liquid crystal element may be a transmissive liquid crystal element,a reflective liquid crystal element, a semi-transmissive liquid crystalelement, or the like.

In the case where a transmissive or semi-transmissive liquid crystalelement is used, two polarizing plates are provided such that a pair ofsubstrates are sandwiched therebetween. Furthermore, a backlight isprovided on the outer side of the polarizing plate. The backlight may bea direct-below backlight or an edge-light backlight. The direct-belowbacklight including a light-emitting diode (LED) is preferably usedbecause local dimming is easily performed to improve contrast. Theedge-light type backlight is preferably used because the thickness of atouch panel module including the backlight can be reduced.

In the case where a reflective liquid crystal element is used, apolarizing plate is provided on a display surface. In addition, a lightdiffusion plate is preferably provided on the display surface to improvevisibility.

[Adhesive Layer]

As the adhesive layer, a variety of curable adhesives such as a reactivecurable adhesive, a thermosetting adhesive, an anaerobic adhesive, and aphoto curable adhesive such as an ultraviolet curable adhesive can beused. Examples of these adhesives include an epoxy resin, an acrylicresin, a silicone resin, a phenol resin, a polyimide resin, an imideresin, a polyvinyl chloride (PVC) resin, a polyvinyl butyral (PVB)resin, and an ethylene vinyl acetate (EVA) resin. In particular, amaterial with low moisture permeability, such as an epoxy resin, ispreferred. Alternatively, a two-component-mixture-type resin may beused. Further alternatively, an adhesive sheet or the like may be used.

Furthermore, the resin may include a drying agent. For example, asubstance that adsorbs water by chemical adsorption, such as oxide of analkaline earth metal (e.g., calcium oxide or barium oxide), can be used.Alternatively, a substance that adsorbs water by physical adsorption,such as zeolite or silica gel, may be used. The drying agent ispreferably included because it can prevent impurities such as water fromentering the element, thereby improving the reliability of the displaypanel.

In addition, it is preferable to mix a filler with a high refractiveindex or light-scattering member into the resin, in which case lightextraction efficiency can be enhanced. For example, titanium oxide,barium oxide, zeolite, zirconium, or the like can be used.

[Connection Layer]

As the connection layers, an anisotropic conductive film (ACF), ananisotropic conductive paste (ACP), or the like can be used.

[Coloring Layer]

Examples of a material that can be used for the coloring layers includea metal material, a resin material, and a resin material containing apigment or dye.

[Light-Blocking Layer]

Examples of a material that can be used for the light-blocking layerinclude carbon black, a metal, a metal oxide, and a composite oxidecontaining a solid solution of a plurality of metal oxides. Stackedfilms containing the material of the coloring layer can also be used forthe light-blocking layer. For example, a stacked-layer structure of afilm containing a material of a coloring layer which transmits light ofa certain color and a film containing a material of a coloring layerwhich transmits light of another color can be employed. It is preferablethat the coloring layer and the light-blocking layer be formed using thesame material because the same manufacturing apparatus can be used andthe process can be simplified.

The above is the description of each of the components.

Structure Example 2

As examples of the display device of one embodiment of the presentinvention, structure examples of an input/output device (touch panel),an input device (touch sensor), and the like will be described below.

Note that in this specification and the like, a display panel as oneembodiment of the display device has a function of displaying(outputting) an image or the like on (to) a display surface; hence, thedisplay panel is one embodiment of an output device.

In this specification and the like, a structure in which a connectorsuch as a flexible printed circuit (FPC) or a tape carrier package (TCP)is attached to a substrate of a display panel, or a structure in whichan integrated circuit (IC) is mounted on a substrate by a chip on glass(COG) method or the like is referred to as a display panel module or adisplay module, or simply referred to as a display panel or the like insome cases.

In this specification and the like, a touch sensor has a function ofsensing contact or approach of an object such as a finger or a stylus;hence, the touch sensor is one embodiment of an input device.

In this specification and the like, a substrate provided with a touchsensor is referred to as a touch sensor panel or simply referred to as atouch sensor or the like in some cases. Furthermore, in thisspecification and the like, a structure in which a connector such as anFPC or a TCP is attached to a substrate of a touch sensor panel, or astructure in which an IC is mounted on a substrate by a COG method orthe like is referred to as a touch sensor panel module, a touch sensormodule, or a sensor module, or simply referred to as a touch sensor orthe like in some cases.

Note that in this specification and the like, a touch panel which is oneembodiment of the display device has a function of displaying(outputting) an image or the like on (to) a display surface and afunction as a touch sensor capable of sensing contact or approach of anobject such as a finger or a stylus on or to the display surface.Therefore, the touch panel is one embodiment of an input/output device.

A touch panel can be referred to, for example, a display panel (or adisplay device) with a touch sensor or a display panel (or a displaydevice) having a touch sensor function.

A touch panel can include a display panel and a touch sensor panel.Alternatively, a touch panel can have a function of a touch sensorinside a display panel.

In this specification and the like, a structure in which a connectorsuch as an FPC or a TCP is attached to a substrate of a touch panel, ora structure in which an IC is mounted on a substrate by a COG method orthe like is referred to as a touch panel module or a display module, orsimply referred to as a touch panel or the like in some cases.

[Structure Example of Touch Sensor]

A structure example of the input device (touch sensor) will be describedbelow with reference to drawings.

FIG. 11A is a schematic top view of an input device 150. The inputdevice 150 includes a plurality of electrodes 151, a plurality ofelectrodes 152, a plurality of wirings 155, and a plurality of wirings156 over a substrate 160. The substrate 160 is provided with a flexibleprinted circuit (FPC) 157 which is electrically connected to each of theplurality of electrodes 151 and the plurality of electrodes 152. FIG.11A illustrates an example in which the FPC 157 is provided with an IC158.

FIG. 11B is an enlarged view of a region surrounded by a dashed dottedline in FIG. 11A. The electrodes 151 are each in the form of a row ofrhombic electrode patterns arranged in a lateral direction of thisfigure. The rhombic electrode patterns aligned in a line areelectrically connected to each other. The electrodes 152 are also eachin the form of a row of rhombic electrode patterns arranged in alongitudinal direction of this figure, and the rhombic electrodepatterns aligned in a line are electrically connected to each other.Part of the electrode 151 and part of the electrode 152 overlap andintersect with each other. At this intersection portion, an insulator issandwiched in order to avoid an electrical short-circuit between theelectrode 151 and the electrode 152.

As illustrated in FIG. 11C, the rhombic electrodes 152 may be connectedwith bridge electrodes 153. The island-shape electrodes 152 are arrangedin the longitudinal direction of the figure, and two adjacent electrodes152 are electrically connected to each other by the bridge electrode153. Such a structure allows the electrodes 151 and the electrodes 152to be formed at the same time by processing the same conductive film.This can prevent variations in the thickness of these electrodes, andcan prevent the resistance value and the light transmittance of eachelectrode from varying from place to place. Note that instead of theelectrodes 152, the electrodes 151 may include the bridge electrodes153.

As illustrated in FIG. 11D, a design in which rhombic electrode patternsof the electrodes 151 and 152 illustrated in FIG. 11B are hollowed outand only edge portions are left may be used. At that time, when theelectrodes 151 and 152 are narrow enough to be invisible to the users,the electrodes 151 and 152 can be formed using a light-blocking materialsuch as a metal or an alloy, as will be described later. In addition,either the electrodes 151 or the electrodes 152 illustrated in FIG. 11Dmay include the above bridge electrodes 153.

One of the electrodes 151 is electrically connected to one of thewirings 155. One of the electrodes 152 is electrically connected to oneof the wirings 156. Here, either one of the electrodes 151 and 152corresponds to a row wiring, and the other corresponds to a columnwiring.

The IC 158 has a function of driving the touch sensor. A signal outputfrom the IC 158 is supplied to either of the electrodes 151 and 152through the wirings 155 or 156. A current (or a potential) flowing toeither of the electrodes 151 and 152 is input to the IC 158 through thewirings 155 or 156.

When a touch panel is formed in such a manner that the input device 150is stacked over a display screen of the display panel, alight-transmitting conductive material is preferably used for theelectrodes 151 and 152. In the case where a light-transmittingconductive material is used for the electrodes 151 and 152 and lightfrom the display panel is extracted through the electrodes 151 or 152,it is preferable that a conductive film containing the same conductivematerial be arranged between the electrodes 151 and 152 as a dummypattern. When part of a space between the electrodes 151 and 152 is thusfilled with the dummy pattern, variation in light transmittance can bereduced. As a result, unevenness in luminance of light transmittedthrough the input device 150 can be reduced.

As the light-transmitting conductive material, a conductive oxide suchas indium oxide, indium tin oxide, indium zinc oxide, zinc oxide, orzinc oxide to which gallium is added can be used. Note that a filmcontaining graphene may be used as well. The film containing graphenecan be formed, for example, by reducing a film containing grapheneoxide. As a reducing method, a method with application of heat or thelike can be employed.

Alternatively, a metal film or an alloy film which is thin enough tohave a light-transmitting property can be used. For example, a metalsuch as gold, silver, platinum, magnesium, nickel, tungsten, chromium,molybdenum, iron, cobalt, copper, palladium, or titanium, or an alloycontaining any of these metals can be used. Alternatively, a nitride ofthe metal or the alloy (e.g., titanium nitride), or the like may beused. Alternatively, a stacked film in which two or more of conductivefilms containing the above materials are stacked may be used.

For the electrodes 151 and 152, a conductive film that is processed tobe thin enough to be invisible to the users may be used. Such aconductive film is processed into a lattice shape (a mesh shape), forexample, which makes it possible to achieve both high conductivity andhigh visibility of the display device. It is preferable that theconductive film have a portion in which the width is greater than orequal to 30 nm and less than or equal to 100 μm, preferably greater thanor equal to 50 nm and less than or equal to 50 μm, and furtherpreferably greater than or equal to 50 nm and less than or equal to 20μm. In particular, the conductive film preferably has a pattern width of10 μm or less because it is hardly visible to the users.

As examples, enlarged schematic views of part of the electrodes 151 or152 are illustrated in FIGS. 12A to 12D. FIG. 12A illustrates an examplewhere a lattice-shape conductive film 146 is used. The conductive film146 is preferably placed so as not to overlap with the display elementincluded in the display device because light from the display device isnot blocked. In that case, it is preferable that the direction of thelattice be the same as the direction of the display element arrangementand that the pitch of the lattice be an integer multiple of the pitch ofthe display element arrangement.

FIG. 12B illustrates an example of a lattice-shape conductive film 147,which is processed so as to be provided with triangle openings. Such astructure makes it possible to further reduce the resistance comparedwith the structure illustrated in FIG. 12A.

In addition, a conductive film 148, which has an irregular patternshape, may be used as illustrated in FIG. 12C. Such a structure canprevent generation of moire when overlapping with the display portion ofthe display device.

Conductive nanowires may be used for the electrodes 151 and 152. FIG.12D illustrates an example where nanowires 149 are used. The nanowires149 are dispersed at appropriate density so as to be in contact with theadjacent nanowires, which can form a two-dimensional network; therefore,the nanowires 149 can function as a conductive film with extremely highlight-transmitting property. For example, nanowires which have a meandiameter of greater than or equal to 1 nm and less than or equal to 100nm, preferably greater than or equal to 5 nm and less than or equal to50 nm, and further preferably greater than or equal to 5 nm and lessthan or equal to 25 nm, can be used. As the nanowire 149, a metalnanowire such as an Ag nanowire, a Cu nanowire, or an Al nanowire, acarbon nanotube, or the like can be used. In the case of using an Agnanowire, a light transmittance of 89% or more and a sheet resistance of40 ohms per square or more and 100 ohms per square or less can beachieved.

The above is the description of structure examples of a touch sensor.

[Structure Example of Touch Panel]

As an example of the display device of one embodiment of the presentinvention, a structure example of a touch panel will be described belowwith reference to drawings.

FIG. 13A is a schematic perspective view of a touch panel 100. FIG. 13Bis a schematic perspective view of a pair of substrates which aredeveloped. Note that only typical components are illustrated forsimplicity. In FIG. 13B, the substrate 31 is illustrated only in dashedoutline.

The touch panel 100 includes the substrate 21 and the substrate 31provided with the input device 150, which are provided to overlap witheach other. For the structure of the substrate 21, the above descriptionof Structure example 1 or the like can be referred to.

For the structure of the input device 150, the above description of thestructure example of the touch sensor can be referred to. FIGS. 13A and13B illustrate an example in which the input device 150 includes theplurality of electrodes 151, the plurality of electrodes 152, theplurality of wirings 155, and the plurality of wirings 156.

As the input device 150, for example, a capacitive touch sensor can beused. Examples of the capacitive touch sensor include a surfacecapacitive touch sensor and a projected capacitive touch sensor.Examples of the projected capacitive touch sensor include aself-capacitive touch sensor and a mutual capacitive touch sensor. Theuse of a mutual capacitive type is preferable because multiple pointscan be sensed simultaneously. An example of using a projected capacitivetouch sensor will be described below.

Note that one embodiment of the present invention is not limited to thisexample, and any of a variety of sensors capable of sensing theproximity or contact of an object to be sensed, such as a finger or astylus, can be used as the input device 150.

In the touch panel 100 illustrated in FIGS. 13A and 13B, the inputdevice 150 is provided on the substrate 31. The wirings 155 and 156 andthe like of the input device 150 are electrically connected to the FPC42 connected to the substrate 21 side through a connection portion 169.

With the above structure, the FPC connected to the touch panel 100 canbe provided only on one substrate side (here, on the substrate 21 side).Although two or more FPCs may be attached to the touch panel 100, forthe simplicity of the structure, the touch panel 100 is preferablyprovided with one FPC 42 which has a function of supplying signals toboth the substrate 21 and the substrate 31 as illustrated in FIGS. 13Aand 13B.

The connection portion 169 can include, for example, an anisotropicconductive connector. As the connector, for example, a conductiveparticle can be used. As the conductive particle, a particle of anorganic resin, silica, or the like coated with a metal material can beused. It is preferable to use nickel or gold as the metal materialbecause contact resistance can be decreased. It is also preferable touse a particle coated with layers of two or more kinds of metalmaterials, such as a particle coated with nickel and further with gold.As the connector, a material capable of elastic deformation or plasticdeformation is preferably used. In that case, the conductive particlesometimes has a shape that is vertically crushed. This increases thecontact area between the connector and a conductive layer electricallyconnected to the connector, thereby reducing contact resistance andsuppressing the generation of problems such as disconnection.

The connector is preferably provided so as to be covered with theadhesive layer 141 (not illustrated) with which the substrates 21 and 31are bonded. For example, the connector may be scattered in theconnection portion 169 after a paste or the like for forming theadhesive layer 141 is applied. A structure in which the connectionportion 169 is provided in a portion where the adhesive layer 141 isprovided can be similarly applied not only to a structure in which theadhesive layer 141 is also provided over the display portion 32 (alsoreferred to as a solid sealing structure) but also to, for example, ahollow sealing structure in which the adhesive layer 141 is provided inthe periphery of a light-emitting device, a liquid crystal displaydevice, or the like.

Unlike in FIG. 1A, an IC 168 is mounted on the FPC 42 in FIGS. 13A and13B. In that case, the IC 168 may have a function of driving the inputdevice 150, or an IC for driving the input device 150 may be separatelyprovided on the substrate 21, the substrate 31, the FPC 42, or the like.

[Cross-Sectional Structural Example]

Next, an example of a cross-sectional structure of the touch panel 100will be described. FIG. 14 is a schematic cross-sectional view of thetouch panel 100. FIG. 14 is different from FIG. 9 mainly in thestructure between the adhesive layer 141 and the substrate 31.

Insulating layers 161, 162, 163, and 164 and the like are stacked on thesurface of the substrate 31 that faces the substrate 21. Alight-blocking layer 133 is provided between the insulating layers 161and 162. The electrodes 151 and 152 and the like are provided betweenthe insulating layers 162 and 163. The bridge electrode 153 is providedbetween the insulating layers 163 and 164. The coloring layers 131 a and131 b, the light-blocking layer 132, and the like are provided on thesurface of the insulating layer 164 that faces the adhesive layer 141.

FIG. 14 clearly shows an intersection of the electrodes 151 and 152.Through openings in the insulating layer 163, the bridge electrode 153is electrically connected to the two electrodes 151 between which theelectrode 152 is positioned.

The electrodes 151 and 152 overlap with the light-blocking layer 132.Also in FIG. 14, the electrode 151 does not overlap with thelight-emitting element 40. In other words, the electrode 151 has a meshshape with an opening overlapping with the light-emitting element 40. Insuch a structure where the electrodes 151 are not arranged on the pathof light emitted from the light-emitting element 40, the electrodes 151do not lead to luminance decrease substantially; thus, a touch panelwith high visibility and low power consumption can be achieved. Notethat the electrode 152 can have a similar structure.

In addition, not overlapping with the light-emitting element 40, theelectrodes 151 and 152 can be formed using a metal material with arelatively low resistance. This increases the sensitivity of the touchsensor as compared to the case where a light-transmitting conductivematerial is used for the electrodes 151 and 152.

FIG. 14 illustrates an example in which the light-blocking layer 133 isprovided between the electrodes 151 and 152 (and the bridge electrode153) and the substrate 31 so as to overlap with the electrodes 151 and152. Even in the case where a metal material is used for the electrode151 and the like, external light reflection on the electrode 151 and thelike can be hindered by the light-blocking layer 133, achieving a touchpanel with higher visibility. Although the two light-blocking layers 132and 133 are provided in this example, either one light-blocking layermay be provided.

The polarizing plate 130 is not necessarily provided over the substrate31, and an object to be sensed, such as a finger or a stylus, may be indirect contact with the substrate 31. In that case, a protective layer(such as a ceramic coat) is preferably provided over the substrate 31.The protective layer can be formed using an inorganic insulatingmaterial such as silicon oxide, aluminum oxide, yttrium oxide, oryttria-stabilized zirconia (YSZ). Alternatively, tempered glass may beused for the substrate 31. Physical or chemical processing by an ionexchange method, a wind tempering method, or the like may be performedon the tempered glass, so that compressive stress is applied on thesurface. In the case where the touch sensor is provided on one side ofthe tempered glass and the opposite side of the tempered glass isprovided on, for example, the outermost surface of an electronic devicefor use as a touch surface, the thickness of the whole device can bedecreased.

When the light-emitting element 40, the plurality of transistors, theelectrodes of the touch sensor, and the like are arranged between thesubstrates 21 and 31 as illustrated in FIG. 14, a touch panel with areduced number of components can be achieved.

Note that the structure of the touch panel 100 is not limited to theabove, and for example, the touch panel may be fabricated by overlappingthe substrate provided with the input device 150 with the display device10 illustrated in FIG. 1 A and the like.

FIG. 15 illustrates an example in which the electrodes 151 and 152 andthe like of the touch sensor are formed on the surface of the substrate31 that is opposite to the surface facing the substrate 21. Thisstructure can be referred to as an on-cell touch panel.

The electrodes 151 and 152 are formed over the substrate 31 and coveredwith the insulating layer 163. The bridge electrode 153 is provided overthe insulating layer 163.

A substrate 170 is a substrate serving as a touch surface, and forexample, serves as part of a housing, protective glass, or the like ofan electronic device where the touch panel is incorporated. Thesubstrates 170 and 31 are bonded with an adhesive layer 165.

FIG. 15 illustrates an example in which the electrode 151 is arrangednot only in a region overlapping with the light-blocking layer 132 butalso in a region overlapping with the light-emitting element 40, thecoloring layer 131 a, and the like. In that case, the electrode 151 canbe formed using a material transmitting visible light. For example, afilm containing a metal oxide, a film containing graphene, or a filmthat contains a metal or an alloy and is thin enough to transmit visiblelight can be used for the electrode 151. The same applies to theelectrode 152. The bridge electrode 153 can also be formed using amaterial transmitting visible light; however, a material blockingvisible light, such as a metal or an alloy, may also be used in the casewhere the bridge electrode 153 overlaps with the light-blocking layer132 or the area of the bridge electrode 153 is extremely small.

The above is the description of the cross-sectional structure example ofthe touch panel.

Structure Example 3

As an example of the display device of one embodiment of the presentinvention, a display device (display panel) that includes both areflective liquid crystal element and a light-emitting element and candisplay an image both in a transmissive mode and in a reflective modewill be described below. Such a display panel can also be referred to asa transmissive OLED and reflective LC hybrid display (TR-hybriddisplay).

One example of such a display panel is a structure in which a liquidcrystal element including an electrode that reflects visible light and alight-emitting element are stacked. In this structure, it is preferablethat the electrode reflecting visible light have an opening and theopening overlap with the light-emitting element. This enables driving inthe transmissive mode by which light is emitted from the light-emittingelement through the opening. It is also preferable that a transistor fordriving the liquid crystal element and a transistor included in thelight-emitting element be positioned on the same plane. In addition, thelight-emitting element and the liquid crystal element are preferablystacked with an insulating layer therebetween.

Such a display panel can be driven with extremely low power consumptionby displaying an image in the reflective mode in a place with brightexternal light such as an outdoor space. At night or in a place withweak external light such an indoor space, the display panel can displayan image with an optimal luminance by displaying the image in thetransmissive mode. Furthermore, by displaying an image in both thetransmissive and reflective modes, the display panel can display theimage with less power consumption and a higher contrast than aconventional display panel even in a place with extremely brightexternal light.

Structure Example

FIG. 16A is a block diagram illustrating an example of the structure ofa display device 200. The display device 200 includes a plurality ofpixels 210 which are arranged in a matrix in the display portion 32. Thedisplay device 200 also includes a circuit GD and a circuit SD. Thedisplay device 200 includes the plurality of pixels 210 arranged in adirection R, and a plurality of wirings Gl, a plurality of wirings G2, aplurality of wirings ANO, and a plurality of wirings CSCOM which areelectrically connected to the circuit GD. The display device 200includes the plurality of pixels 210 arranged in a direction C, and aplurality of wirings S1 and a plurality of wirings S2 which areelectrically connected to the circuit SD.

The pixel 210 includes a reflective liquid crystal element and alight-emitting element. In the pixel 210, the liquid crystal element andthe light emitting element partly overlap with each other.

FIG. 16B1 illustrates a structure example of a conductive layer 191included in the pixel 210. The conductive layer 191 serves as areflective electrode of the liquid crystal element in the pixel 210. Theconductive layer 191 includes an opening 251.

In FIG. 16B1, the light-emitting element 40 in a region overlapping withthe conductive layer 191 is denoted by a dashed line. The light-emittingelement 40 overlaps with the opening 251 included in the conductivelayer 191. Thus, light from the light-emitting element 40 is emitted toa display surface side through the opening 251.

In FIG. 16B1, the pixels 210 adjacent in the direction R correspond todifferent colors. As illustrated in FIG. 16B1, the openings 251 arepreferably provided in different positions in the conductive layers 191so as not to be aligned in the two pixels adjacent to each other in thedirection R. This allows the two light-emitting elements 40 to be apartfrom each other, thereby preventing light emitted from thelight-emitting element 40 from entering a coloring layer in the adjacentpixel 210 (such a phenomenon is also referred to as crosstalk).Furthermore, since the two adjacent light-emitting elements 40 can bearranged apart from each other, a high-resolution display device isachieved even when EL layers of the light-emitting elements 40 areseparately formed with a shadow mask or the like.

Alternatively, arrangement illustrated in FIG. 16B2 may be employed.

If the ratio of the total area of the opening 251 to the total areaexcept for the opening is too large, display performed using the liquidcrystal element is dark. If the ratio of the total area of the opening251 to the total area except for the opening is too small, displayperformed using the light-emitting element 40 is dark.

If the area of the opening 251 in the conductive layer 191 serving as areflective electrode is too small, light emitted from the light-emittingelement 40 is not efficiently extracted for display.

The opening 251 may have a polygonal shape, a quadrangular shape, anelliptical shape, a circular shape, a cross-like shape, a stripe shape,a slit-like shape, or a checkered pattern, for example. The opening 251may be close to the adjacent pixel. Preferably, the opening 251 isprovided close to another pixel emitting light of the same color, inwhich case crosstalk can be suppressed.

[Circuit Structure Example]

FIG. 17 is a circuit diagram illustrating a structure example of thepixel 210. FIG. 17 shows two adjacent pixels 210.

The pixel 210 includes a switch SW1, a capacitor C1, the liquid crystalelement 60, a switch SW2, a transistor M, a capacitor C2, thelight-emitting element 40, and the like. The pixel 210 is electricallyconnected to the wiring Gl, the wiring G2, the wiring ANO, the wiringCSCOM, the wiring S1, and the wiring S2. FIG. 17 also illustrates awiring VCOM1 electrically connected to the liquid crystal element 60 anda wiring VCOM2 electrically connected to the light-emitting element 40.

FIG. 17 illustrates an example in which a transistor is used as each ofthe switches SW1 and SW2.

A gate of the switch SW1 is connected to the wiring G1. One of a sourceand a drain of the switch SW1 is connected to the wiring S and the otherof the source and the drain is connected to one electrode of thecapacitor C1 and one electrode of the liquid crystal element 60. Theother electrode of the capacitor C1 is connected to the wiring CSCOM.The other electrode of the liquid crystal element 60 is connected to thewiring VCOM1.

A gate of the switch SW2 is connected to the wiring G2. One of a sourceand a drain of the switch SW2 is connected to the wiring S2, and theother of the source and the drain is connected to one electrode of thecapacitor C2 and a gate of the transistor M. The other electrode of thecapacitor C2 is connected to one of a source and a drain of thetransistor M and the wiring ANO. The other of the source and the drainof the transistor M is connected to one electrode of the light-emittingelement 40. The other electrode of the light-emitting element 40 isconnected to the wiring VCOM2.

FIG. 17 illustrates an example in which the transistor M includes twogates between which a semiconductor is provided and which are connectedto each other. This structure can increase the amount of current flowingthrough the transistor M.

The wiring G1 can be supplied with a signal for changing the on/offstate of the transistor SW1. A predetermined potential can be suppliedto the wiring VCOM1. The wiring S1 can be supplied with a signal forchanging the orientation of liquid crystals of the liquid crystalelement 60. A predetermined potential can be supplied to the wiringCSCOM.

The wiring G2 can be supplied with a signal for changing the on/offstate of the transistor SW2. The wiring VCOM2 and the wiring ANO can besupplied with potentials having a difference large enough to make thelight-emitting element 40 emit light. The wiring S2 can be supplied witha signal for changing the on/off state of the transistor M.

In the pixel 210 of FIG. 17, for example, an image can be displayed inthe reflective mode by driving the pixel with the signals supplied tothe wiring G1 and the wiring Si and utilizing the optical modulation ofthe liquid crystal element 60. In the case where an image is displayedin the transmissive mode, the pixel is driven with the signals suppliedto the wiring G2 and the wiring S2 and the light-emitting element 40emits light. In the case where both modes are performed at the sametime, the pixel can be driven with the signals to the wiring GI, thewiring G2, the wiring SI, and the wiring S2.

[Cross-Sectional Structure Example of Display Device]

FIG. 18 is a schematic cross-sectional view of the display device 200.

The display device 200 includes an insulating layer 220 between thesubstrates 21 and 31. The display device 200 also includes thelight-emitting element 40, the transistor 205, a transistor 206, acoloring layer 134, and the like between the substrate 21 and theinsulating layer 220. Furthermore, the display device 200 includes theliquid crystal element 60, a coloring layer 131, the structure body 11,and the like between the substrate 31 and the insulating layer 220.

The substrate 21 and the insulating layer 220 are bonded with theadhesive layer 141. The substrate 31 and the insulating layer 220 arebonded with an adhesive layer 142 with which a liquid crystal is sealed.

The liquid crystal element 60 is a reflective liquid crystal element.The liquid crystal element 60 has a stacked structure of a conductivelayer 192, a liquid crystal 193, and a conductive layer 194. Theconductive layer 191 is provided in contact with the surface of theconductive layer 192 that faces the substrate 21. The conductive layer191 serves as a reflective electrode of the liquid crystal element 60.The conductive layer 191 includes the opening 251. The conductive layer192 contains a material transmitting visible light.

The light-emitting element 40 is a bottom-emission light-emittingelement. The light-emitting element 40 has a structure in which theconductive layer Ill, the EL layer 112, and the conductive layer 113 arestacked in this order from the side of the insulating layer 220. Theconductive layer 113 contains a material reflecting visible light, andthe conductive layer 111 contains a material transmitting visible light.Light is emitted from the light-emitting element 40 to the substrate 31side through the coloring layer 134, the insulating layer 220, theopening 251, the conductive layer 192, and the like.

A structure body 12 is provided on the insulating layer 216 covering anend portion of the conductive layer 111. The structure body 12 has afunction as a spacer for preventing the insulating layer 220 and thesubstrate 21 from getting closer more than necessary. The structure body12 is not necessarily provided.

One of the source and the drain of the transistor 205 is electricallyconnected to the conductive layer 111 of the light-emitting element 40.The transistor 205 corresponds to, for example, the transistor M in FIG.17.

One of a source and a drain of the transistor 206 is electricallyconnected to the conductive layers 191 and 192 through a terminalportion 207. That is, the terminal portion 207 electrically connects theconductive layers provided on both surfaces of the insulating layer 220through openings in the insulating layer 220 in the display portion 32.The transistor 206 corresponds to, for example, the switch SW1 in FIG.17.

The terminal portion 204 is provided in a region where the substrates 21and 31 do not overlap with each other. Similarly to the terminal portion207, the terminal portion 204 electrically connects the conductivelayers provided on both surfaces of the insulating layer 220. On the topsurface of the terminal portion 204, a conductive layer obtained byprocessing the same conductive film as the conductive layer 192 isexposed. Thus, the terminal portion 204 and the FPC 42 can beelectrically connected to each other through the connection layer 242.

The coloring layer 131 and the light-blocking layer 132 are provided onthe surface of the substrate 31 that faces the substrate 21. Inaddition, an insulating layer 195 is provided to cover the coloringlayer 131 and the light-blocking layer 132. The insulating layer 195serves as an overcoat. The conductive layer 194 is provided on thesurface of the insulating layer 195 that faces the substrate 21.

A connection portion 252 is provided in part of a region where theadhesive layer 142 is provided. In the connection portion 252, theconductive layer obtained by processing the same conductive film as theconductive layer 192 and part of the conductive layer 194 areelectrically connected with a connector 243. Accordingly, a signal or apotential input from the FPC 42 connected to the substrate 21 side canbe supplied to the conductive layer 194 formed on the substrate 31 sidethrough the connection portion 252.

The structure body 11 is provided between the conductive layers 192 and194. The structure body 11 has a function of maintaining a cell gap ofthe liquid crystal element 60. Here, the structure body 11 is formed onthe substrate 31 side, which is opposite to the side shown in FIG. 7A.The surface of the insulating layer 195 has a depression, and thestructure body 11 is formed to overlap with the depression. The topsurface (part of the surface on the display surface side) of thestructure body 11 is positioned above the bottom surface of the coloringlayer 131. This can reduce the distance between the substrates 21 and 31and improve viewing angle characteristics.

Although not illustrated here, an alignment film for adjusting thealignment of the liquid crystal 193 may be provided between theconductive layer 194 and the liquid crystal 193 and between theconductive layer 192 and the liquid crystal 193. In that case, part ofthe alignment film may be provided to cover the surface of the structurebody 11.

An example of the method for manufacturing the display device 200 isdescribed. For example, the conductive layer 192, the conductive layer191, and the insulating layer 220 are formed in order over a supportingsubstrate provided with a separation layer, and the transistor 205, thelight-emitting element 40, and the like are formed. Then, the substrate21 and the supporting substrate are bonded with the adhesive layer 141.After that, separation is performed at the interface between theseparation layer and each of the insulating layer 220 and the conductivelayer 192, whereby the supporting substrate and the separation layer areremoved. Separately, the coloring layer 131, the light-blocking layer132, the structure body 11, and the like are formed over the substrate31 in advance. Then, the liquid crystal 193 is dropped onto thesubstrate 21 or 31 and the substrates 21 and 31 are bonded with theadhesive layer 142, whereby the display device 200 can be manufactured.

A material for the separation layer can be selected such that separationat the interface with the insulating layer 220 and the conductive layer192 occurs. In particular, it is preferable that a stacked layer of alayer including a high-melting-point metal material, such as tungsten,and a layer including an oxide of the metal material be used as theseparation layer, and a stacked layer of a plurality of layers, such asa silicon nitride layer, a silicon oxynitride layer, and a siliconnitride oxide layer be used as the insulating layer 220 over theseparation layer. The use of the high-melting-point metal material forthe separation layer can increase the formation temperature of a layerformed in a later step, which reduces impurity concentration andachieves a highly reliable display device.

As the conductive layer 192, a metal oxide, a metal nitride, or an oxidesuch as an oxide semiconductor whose resistance is reduced is preferablyused. In the case of using an oxide semiconductor, a material in whichat least one of the concentrations of hydrogen, boron, phosphorus,nitrogen, and other impurities and the number of oxygen vacancies ismade to be higher than those in a semiconductor layer of a transistor isused for the conductive layer 192.

The above is the description of Structure example 3.

At least part of this embodiment can be implemented in combination withany of the other embodiments described in this specification asappropriate.

Embodiment 2

Described in this embodiment is an example of a driving method of aninput device (touch sensor) which can be applied to the display deviceof one embodiment of the present invention.

FIG. 19A is a block diagram illustrating the structure of a mutualcapacitive touch sensor. FIG. 19A illustrates a pulse voltage outputcircuit 601 and a current sensing circuit 602. Note that in FIG. 19A,six wirings X1 to X6 represent electrodes 621 to which a pulse voltageis applied, and six wirings Y1 to Y6 represent electrodes 622 that sensechanges in current. The number of such electrodes is not limited tothose illustrated in this example. FIG. 19A also illustrates a capacitor603 that is formed with the electrodes 621 and 622 overlapping with eachother or being provided close to each other. Note that functionalreplacement between the electrodes 621 and 622 is possible.

For example, the electrode 151 described in Embodiment 1 corresponds toone of the electrodes 621 and 622, and the electrode 152 described inEmbodiment 1 corresponds to the other of the electrodes 621 and 622.

The pulse voltage output circuit 601 is, for example, a circuit forsequentially inputting a pulse voltage to the wirings X1 to X6. Thecurrent sensing circuit 602 is, for example, a circuit for sensingcurrent flowing through each of the wirings Y1-Y6.

By application of a pulse voltage to one of the wirings X1 to X6, anelectric field is generated between the electrodes 621 and 622 of thecapacitor 603, and current flows through the electrode 622. Part of theelectric field generated between the electrodes is blocked when anobject such a finger or a stylus contacts or approaches the device, sothat the electric field intensity between the electrodes is changed.Consequently, the amount of current flowing through the electrode 622 ischanged.

For example, in the case where there is no approach or no contact of anobject, the amount of current flowing in each of the wirings Y1-Y6depends on the amount of capacitance of the capacitor 603. In the casewhere part of an electric field is blocked by the approach or contact ofan object, a decrease in the amount of current flowing in the wiringsY1-Y6 is sensed. The approach or contact of an object can be sensed byutilizing this change.

Sensing by the current sensing circuit 602 may be performed using anintegral value (time integral value) of current flowing in a wiring. Inthat case, sensing may be performed with an integrator circuit, forexample. Alternatively, the peak current value may be sensed. In thatcase, for example, current may be converted into voltage, and the peakvoltage value may be sensed.

FIG. 19B is an example of a timing chart illustrating input and outputwaveforms in the mutual capacitive touch sensor in FIG. 19A. In FIG.19B, sensing in each row and each column is performed in one sensingperiod. FIG. 19B shows a period when the contact or approach of anobject is not sensed (when the touch sensor is not touched) and a periodwhen the contact or approach of an object is sensed (when the touchsensor is touched). Here, the wirings Y l -Y6 each show a waveform of avoltage corresponding to the amount of current to be sensed.

As shown in FIG. I9B, the wirings X1-X6 are sequentially supplied with apulse voltage. Accordingly, current flows in the wirings Y1-Y6. When thetouch sensor is not touched, substantially the same current flows in thewirings Y1-Y6 in accordance with a change in voltages of the wiringsX1-X6; thus, the wirings Yl-Y6 have similar output waveforms. Meanwhile,when the touch sensor is touched, current flowing in a wiring in aposition which an object contacts or approaches among the wirings Y1-Y6is reduced; thus, the output waveforms are changed as shown in FIG. 19B.

FIG. 19B shows an example in which an object contacts or approaches theintersection of the wiring X3 and the wiring Y3 or the vicinity thereof.

A change in current due to block of an electric field generated betweena pair of electrodes is sensed in this manner in a mutual capacitivetouch sensor, so that positional information of an object can beobtained. When the detection sensitivity is high, the coordinates of theobject can be determined even when the object is far from a detectionsurface (e.g., a surface of the touch panel).

By driving a touch panel by a method in which a display period of adisplay portion and a sensing period of a touch sensor do not overlapwith each other, the detection sensitivity of the touch sensor can beincreased. For example, a display period and a sensing period may beseparately provided in one display frame period. In that case, two ormore sensing periods are preferably provided in one frame period. Whenthe frequency of sensing is increased, the detection sensitivity can beincreased.

It is preferable that, as an example, the pulse voltage output circuit601 and the current sensing circuit 602 be formed in an IC. For example,the IC is preferably mounted on a touch panel or a substrate in ahousing of an electronic device. In the case where the touch panel hasflexibility, parasitic capacitance might be increased in a bent portionof the touch panel, and the influence of noise might be increased. Inview of this, it is preferable to use an IC to which a driving methodless influenced by noise is applied. For example, it is preferable touse an IC to which a driving method capable of increasing a signal-noiseratio (SIN ratio) is applied.

At least part of this embodiment can be implemented in combination withany of the other embodiments described in this specification asappropriate.

Embodiment 3

In this embodiment, an example of a transistor that can be used as thetransistors described in the above embodiments will be described withreference to drawings.

The display device of one embodiment of the present invention can befabricated by using a transistor with any of various modes, such as abottom-gate transistor or a top-gate transistor. Therefore, a materialfor a semiconductor layer or the structure of a transistor can be easilychanged in accordance with the existing production line.

[Bottom-Gate Transistor]

FIG. 20A1 is a cross-sectional view of a transistor 810 that is achannel-protective transistor, which is a type of bottom-gatetransistor. In FIG. 20A1, the transistor 810 is formed over a substrate771. The transistor 810 includes an electrode 746 over the substrate 771with an insulating layer 772 provided therebetween. The transistor 810includes a semiconductor layer 742 over the electrode 746 with aninsulating layer 726 provided therebetween. The electrode 746 can serveas a gate electrode. The insulating layer 726 can serve as a gateinsulating layer.

The transistor 810 includes an insulating layer 741 over a channelformation region in the semiconductor layer 742. The transistor 810includes an electrode 744 a and an electrode 744 b which are partly incontact with the semiconductor layer 742 and over the insulating layer726. The electrode 744 a can serve as one of a source electrode and adrain electrode. The electrode 744 b can serve as the other of thesource electrode and the drain electrode. Part of the electrode 744 aand part of the electrode 744 b are formed over the insulating layer741.

The insulating layer 741 can serve a channel protective layer. With theinsulating layer 741 provided over the channel formation region, thesemiconductor layer 742 can be prevented from being exposed at the timeof forming the electrodes 744 a and 744 b. Thus, the channel formationregion in the semiconductor layer 742 can be prevented from being etchedat the time of forming the electrodes 744 a and 744 b. According to oneembodiment of the present invention, a transistor with favorableelectrical characteristics can be provided.

The transistor 810 includes an insulating layer 728 over the electrode744 a, the electrode 744 b, and the insulating layer 741 and furtherincludes an insulating layer 729 over the insulating layer 728.

For example, the insulating layer 772 can be formed using a material anda method similar to those of insulating layers 722 and 705. Note thatthe insulating layer 772 may be formed of a stack of insulating layers.For example, the semiconductor layer 742 can be formed using a materialand a method similar to those of the semiconductor layer 708. Note thatthe semiconductor layer 742 may be formed of a stack of semiconductorlayers. For example, the electrode 746 can be formed using a materialand a method similar to those of the electrode 706. Note that theelectrode 746 may be formed of a stack of conductive layers. Theinsulating layer 726 can be formed using a material and a method similarto those of the insulating layer 707. Note that the insulating layer 726may be formed of a stack of insulating layers. For example, theelectrodes 744 a and 744 b can be formed using a material and a methodsimilar to those of the electrode 714 or 715. Note that the electrodes744 a and 744 b may be formed of a stack of conductive layers. Forexample, the insulating layer 741 can be formed using a material and amethod similar to those of the insulating layer 726. Note that theinsulating layer 741 may be formed of a stack of insulating layers. Forexample, the insulating layer 728 can be formed using a material and amethod similar to those of the insulating layer 710. Note that theinsulating layer 728 may be formed of a stack of insulating layers. Forexample, the insulating layer 729 can be formed using a material and amethod similar to those of the insulating layer 711. Note that theinsulating layer 729 may be formed of a stack of insulating layers.

The electrode, the semiconductor layer, the insulating layer, and thelike used in the transistor disclosed in this embodiment can be formedusing a material and a method disclosed in any of the other embodiments.

In the case where an oxide semiconductor is used for the semiconductorlayer 742, a material capable of removing oxygen from part of thesemiconductor layer 742 to generate oxygen vacancies is preferably usedfor regions of the electrodes 744 a and 744 b that are in contact withat least the semiconductor layer 742. The carrier concentration in theregions of the semiconductor layer 742 where oxygen vacancies aregenerated is increased, so that the regions become n-type regions (n⁺layers). Accordingly, the regions can serve as a source region and adrain region. When an oxide semiconductor is used for the semiconductorlayer 742, examples of the material capable of removing oxygen from thesemiconductor layer 742 to generate oxygen vacancies include tungstenand titanium.

Formation of the source region and the drain region in the semiconductorlayer 742 makes it possible to reduce the contact resistance between thesemiconductor layer 742 and each of the electrodes 744 a and 744 b.Accordingly, the electric characteristics of the transistor, such as thefield-effect mobility and the threshold voltage, can be favorable.

In the case where a semiconductor such as silicon is used for thesemiconductor layer 742, a layer that serves as an n-type semiconductoror a p-type semiconductor is preferably provided between thesemiconductor layer 742 and the electrode 744 a and between thesemiconductor layer 742 and the electrode 744 b. The layer that servesas an n-type semiconductor or a p-type semiconductor can serve as thesource region or the drain region in the transistor.

The insulating layer 729 is preferably formed using a material that canprevent or reduce diffusion of impurities into the transistor from theoutside. The insulating layer 729 is not necessarily formed.

When an oxide semiconductor is used for the semiconductor layer 742,heat treatment may be performed before and/or after the insulating layer729 is formed. The heat treatment can fill oxygen vacancies in thesemiconductor layer 742 by diffusing oxygen contained in the insulatinglayer 729 or other insulating layers into the semiconductor layer 742.Alternatively, the insulating layer 729 may be formed while the heattreatment is performed, so that oxygen vacancies in the semiconductorlayer 742 can be filled.

Note that a CVD method can be generally classified into a plasmaenhanced CVD (PECVD) method using plasma, a thermal CVD (TCVD) methodusing heat, and the like. A CVD method can be further classified into ametal CVD (MCVD) method, a metal organic CVD (MOCVD) method, and thelike according to a source gas to be used.

Furthermore, an evaporation method can be generally classified into aresistance heating evaporation method, an electron beam evaporationmethod, a molecular beam epitaxy (MBE) method, a pulsed laser deposition(PLO) method, an ion beam assisted deposition (IBAD) method, an atomiclayer deposition (ALD) method, and the like.

By using a PECVD method, a high-quality film can be formed at arelatively low temperature. By using a deposition method that does notuse plasma for deposition, such as an MOCVD method or an evaporationmethod, a film with few defects can be formed because damage is noteasily caused on a surface on which the film is deposited.

A sputtering method is generally classified into a DC sputtering method,a magnetron sputtering method, an RF sputtering method, an ion beamsputtering method, an electron cyclotron resonance (ECR) sputteringmethod, a facing-target sputtering method, and the like.

In the facing-target sputtering method, plasma is confined betweentargets; thus, plasma damage to a substrate can be reduced. Furthermore,step coverage can be improved because the incident angle of a sputteredparticle to a substrate can be made smaller depending on the inclinationof a target.

A transistor 811 illustrated in FIG. 20A2 is different from thetransistor 810 in that an electrode 723 that can serve as a back gateelectrode is provided over the insulating layer 729. The electrode 723can be formed using a material and a method similar to those of theelectrode 746.

In general, the back gate electrode is formed using a conductive layerand positioned so that a channel formation region of a semiconductorlayer is positioned between the gate electrode and the back gateelectrode. Thus, the back gate electrode can function in a mannersimilar to that of the gate electrode. The potential of the back gateelectrode may be the same as that of the gate electrode or may be aground (GND) potential or a predetermined potential. By changing thepotential of the back gate electrode independently of the potential ofthe gate electrode, the threshold voltage of the transistor can bechanged.

The electrode 746 and the electrode 723 can each serve as a gateelectrode. Thus, the insulating layers 726, 728, and 729 can each serveas a gate insulating layer. The electrode 723 may also be providedbetween the insulating layers 728 and 729.

In the case where one of the electrodes 746 and 723 is referred to as a“gate electrode”, the other is referred to as a “back gate electrode”.For example, in the transistor 811, in the case where the electrode 723is referred to as a “gate electrode”, the electrode 746 is referred toas a “back gate electrode”. In the case where the electrode 723 is usedas a “gate electrode”, the transistor 811 can be regarded as a kind oftop-gate transistor. Alternatively, one of the electrodes 746 and 723may be referred to as a “first gate electrode”, and the other may bereferred to as a “second gate electrode”.

By providing the electrodes 746 and 723 with the semiconductor layer 742provided therebetween and setting the potentials of the electrodes 746and 723 to be the same, a region of the semiconductor layer 742 throughwhich carriers flow is enlarged in the film thickness direction; thus,the number of transferred carriers is increased. As a result, theon-state current and field-effect mobility of the transistor 811 areincreased.

Therefore, the transistor 811 has a high on-state current for its area.That is, the area of the transistor 811 can be small for a requiredon-state current. According to one embodiment of the present invention,the area occupied by a transistor can be reduced. Therefore, accordingto one embodiment of the present invention, a semiconductor devicehaving a high degree of integration can be provided.

The gate electrode and the back gate electrode are formed usingconductive layers and thus each have a function of preventing anelectric field generated outside the transistor from influencing thesemiconductor layer in which the channel is formed (in particular, anelectric field blocking function against static electricity and thelike). When the back gate electrode is formed larger than thesemiconductor layer such that the semiconductor layer is covered withthe back gate electrode, the electric field blocking function can beenhanced.

Since the electrodes 746 and 723 each have a function of blocking anelectric field generated outside, electric charge of charged particlesand the like generated on the insulating layer 772 side or above theelectrode 723 do not influence the channel formation region in thesemiconductor layer 742. Thus, degradation by a stress test (e.g., anegative gate bias temperature (-GBT) stress test in which negativeelectric charge is applied to a gate) can be reduced. Furthermore, achange in gate voltage (rising voltage) at which on-state current startsflowing depending on drain voltage can be reduced. Note that this effectis obtained when the electrodes 746 and 723 have the same potential ordifferent potentials.

The BT stress test is one kind of acceleration test and can evaluate, ina short time, a change by long-term use (i.e., a change over time) incharacteristics of a transistor. In particular, the amount of change inthe threshold voltage of a transistor before and after the BT stresstest is an important indicator when examining the reliability of thetransistor. As the change in threshold voltage is smaller, thetransistor has higher reliability.

By providing the electrodes 746 and 723 and setting the potentials ofthe electrodes 746 and 723 to be the same, the amount of change inthreshold voltage is reduced. Accordingly, variations in electricalcharacteristics among a plurality of transistors are also reduced.

A transistor including a back gate electrode has a smaller change inthreshold voltage before and after a positive GBT stress test, in whichpositive electric charge is applied to a gate, than a transistorincluding no back gate electrode.

When the back gate electrode is formed using a light-blocking conductivefilm, light can be prevented from entering the semiconductor layer fromthe back gate electrode side. Therefore, photodegradation of thesemiconductor layer can be prevented, and deterioration in electricalcharacteristics of the transistor, such as a shift of the thresholdvoltage, can be prevented.

According to one embodiment of the present invention, a transistor withhigh reliability can be provided. Moreover, a semiconductor device withhigh reliability can be provided.

FIG. 20B1 is a cross-sectional view of a channel-protective transistor820 that is a type of bottom-gate transistor. The transistor 820 hassubstantially the same structure as the transistor 810 but is differentfrom the transistor 810 in that the insulating layer 741 covers an endportion of the semiconductor layer 742. The semiconductor layer 742 iselectrically connected to the electrode 744 a through an opening formedby selectively removing part of the insulating layer 741 which overlapswith the semiconductor layer 742. The semiconductor layer 742 iselectrically connected to the electrode 744 b through another openingformed by selectively removing part of the insulating layer 741 whichoverlaps with the semiconductor layer 742. A region of the insulatinglayer 741 which overlaps with the channel formation region can serve asa channel protective layer.

A transistor 821 illustrated in FIG. 20B2 is different from thetransistor 820 in that the electrode 723 that can serve as a back gateelectrode is provided over the insulating layer 729.

With the insulating layer 741, the semiconductor layer 742 can beprevented from being exposed at the time of forming the electrodes 744 aand 744 b. Thus, the semiconductor layer 742 can be prevented from beingreduced in thickness at the time of forming the electrodes 744 a and 744b.

The length between the electrode 744 a and the electrode 746 and thelength between the electrode 744 b and the electrode 746 in thetransistors 820 and 821 are larger than those in the transistors 810 and811. Thus, the parasitic capacitance generated between the electrode 744a and the electrode 746 can be reduced. Moreover, the parasiticcapacitance generated between the electrode 744 b and the electrode 746can be reduced. According to one embodiment of the present invention, atransistor with favorable electrical characteristics can be provided.

A transistor 825 illustrated in FIG. 20C1 is a channel-etched transistorthat is a type of bottom-gate transistor. In the transistor 825, theelectrodes 744 a and 744 b are formed without providing the insulatinglayer 741. Thus, part of the semiconductor layer 742 that is exposed atthe time of forming the electrodes 744 a and 744 b is etched in somecases. However, since the insulating layer 741 is not provided, theproductivity of the transistor can be increased.

A transistor 826 illustrated in FIG. 20C2 is different from thetransistor 825 in that the electrode 723 which can serve as a back gateelectrode is provided over the insulating layer 729.

[Top-Gate Transistor]

FIG. 21A1 is a cross-sectional view of a transistor 830 that is a typeof top-gate transistor. The transistor 830 includes the semiconductorlayer 742 over the insulating layer 772, the electrodes 744 a and 744 bthat are over the semiconductor layer 742 and the insulating layer 772and in contact with part of the semiconductor layer 742, the insulatinglayer 726 over the semiconductor layer 742 and the electrodes 744 a and744 b, and the electrode 746 over the insulating layer 726.

Since the electrode 746 overlaps with neither the electrode 744 a northe electrode 744 b in the transistor 830, the parasitic capacitancegenerated between the electrodes 746 and 744 a and the parasiticcapacitance generated between the electrodes 746 and 744 b can bereduced. After the formation of the electrode 746, an impurity 755 isintroduced into the semiconductor layer 742 using the electrode 746 as amask, so that an impurity region can be formed in the semiconductorlayer 742 in a self-aligned manner (see FIG. 21A3). According to oneembodiment of the present invention, a transistor with favorableelectrical characteristics can be provided.

The introduction of the impurity 755 can be performed with an ionimplantation apparatus, an ion doping apparatus, or a plasma treatmentapparatus.

As the impurity 755, for example, at least one kind of element of Group13 elements and Group 15 elements can be used. In the case where anoxide semiconductor is used for the semiconductor layer 742, it ispossible to use at least one kind of element of a rare gas, hydrogen,and nitrogen as the impurity 755.

A transistor 831 illustrated in FIG. 21A2 is different from thetransistor 830 in that the electrode 723 and the insulating layer 727are included. The transistor 831 includes the electrode 723 formed overthe insulating layer 772 and the insulating layer 727 formed over theelectrode 723. The electrode 723 can serve as a back gate electrode.Thus, the insulating layer 727 can serve as a gate insulating layer. Theinsulating layer 727 can be formed using a material and a method similarto those of the insulating layer 726.

Like the transistor 811, the transistor 831 has a high on-state currentfor its area. That is, the area of the transistor 831 can be small for arequired on-state current. According to one embodiment of the presentinvention, the area occupied by a transistor can be reduced. Therefore,according to one embodiment of the present invention, a semiconductordevice having a high degree of integration can be provided.

A transistor 840 illustrated in FIG. 21B1 is a type of top-gatetransistor. The transistor 840 is different from the transistor 830 inthat the semiconductor layer 742 is formed after the formation of theelectrodes 744 a and 744 b. A transistor 841 illustrated in FIG. 21B2 isdifferent from the transistor 840 in that the electrode 723 and theinsulating layer 727 are included. In the transistors 840 and 841, partof the semiconductor layer 742 is formed over the electrode 744 a andanother part of the semiconductor layer 742 is formed over the electrode744 b.

Like the transistor 811, the transistor 841 has a high on-state currentfor its area. That is, the area of the transistor 841 can be small for arequired on-state current. According to one embodiment of the presentinvention, the area occupied by a transistor can be reduced. Therefore,according to one embodiment of the present invention, a semiconductordevice having a high degree of integration can be provided.

A transistor 842 illustrated in FIG. 22A1 is a type of top-gatetransistor. The transistor 842 is different from the transistor 830 or840 in that the electrodes 744 a and 744 b are formed after theformation of the insulating layer 729. The electrodes 744 a and 744 bare electrically connected to the semiconductor layer 742 throughopenings formed in the insulating layers 728 and 729.

Part of the insulating layer 726 that does not overlap with theelectrode 746 is removed, and the impurity 755 is introduced into thesemiconductor layer 742 using the electrode 746 and the insulating layer726 that is left as a mask, so that an impurity region can be formed inthe semiconductor layer 742 in a self-aligned manner (see FIG. 22A3).The transistor 842 includes a region where the insulating layer 726extends beyond an end portion of the electrode 746. The semiconductorlayer 742 in a region into which the impurity 755 is introduced throughthe insulating layer 726 has a lower impurity concentration than thesemiconductor layer 742 in a region into which the impurity 755 isintroduced without through the insulating layer 726. Thus, a lightlydoped drain (LDD) region is formed in a region adjacent to a portion ofthe semiconductor layer 742 which overlaps with the electrode 746.

A transistor 843 illustrated in FIG. 22A2 is different from thetransistor 842 in that the electrode 723 is included. The transistor 843includes the electrode 723 that is formed over the substrate 771 andoverlaps with the semiconductor layer 742 with the insulating layer 772provided therebetween. The electrode 723 can serve as a back gateelectrode.

As in a transistor 844 illustrated in FIG. 22B1 and a transistor 845illustrated in FIG. 22B2, the insulating layer 726 in a region that doesnot overlap with the electrode 746 may be completely removed.Alternatively, as in a transistor 846 illustrated in FIG. 22C1 and atransistor 847 illustrated in FIG. 22C2, the insulating layer 726 may beleft.

In the transistors 842 to 847, after the formation of the electrode 746,the impurity 755 is introduced into the semiconductor layer 742 usingthe electrode 746 as a mask, so that an impurity region can be formed inthe semiconductor layer 742 in a self-aligned manner. According to oneembodiment of the present invention, a transistor with favorableelectrical characteristics can be provided. Furthermore, according toone embodiment of the present invention, a semiconductor device having ahigh degree of integration can be provided.

At least part of this embodiment can be implemented in combination withany of the other embodiments described in this specification asappropriate.

Embodiment 4

In this embodiment, a display module and electronic devices that includethe display device of one embodiment of the present invention will bedescribed with reference to drawings.

In a display module 8000 illustrated in FIG. 23, a touch panel 8004connected to an FPC 8003, a frame 8009, a printed board 8010, and abattery 8011 are provided between an upper cover 8001 and a lower cover8002.

The display panel, the touch panel, or the touch panel module of oneembodiment of the present invention can be used for, for example, thetouch panel 8004.

The shapes and sizes of the upper cover 8001 and the lower cover 8002can be changed as appropriate in accordance with the size of the touchpanel 8004.

The touch panel 8004 can be a resistive touch panel or a capacitivetouch panel and may be formed so as to overlap with a display panel. Acounter substrate (sealing substrate) of the touch panel 8004 can have atouch panel function. A photosensor may be provided in each pixel of thetouch panel 8004 so that an optical touch panel can be obtained.

In the case where a transmissive or a semi-transmissive liquid crystalelement is used, a backlight may be provided between the touch panel8004 and the frame 8009. The backlight includes a light source. Notethat the light source may be provided over the backlight; alternatively,the light source may be provided at an end portion of the backlight anda light diffusion plate may be further provided. Note that the backlightneed not be provided in the case where a self-luminous light-emittingelement such as an organic EL element is used or in the case where areflective panel or the like is employed.

The frame 8009 protects the touch panel 8004 and also serves as anelectromagnetic shield for blocking electromagnetic waves generated bythe operation of the printed board 8010. The frame 8009 can also serveas a radiator plate.

The printed board 8010 is provided with a power supply circuit and asignal processing circuit for outputting a video signal and a clocksignal. As a power source for supplying electric power to the powersupply circuit, an external commercial power source or a power sourceusing the battery 8011 provided separately may be used. The battery 8011can be omitted in the case of using a commercial power source.

The touch panel 8004 can be additionally provided with a component suchas a polarizing plate, a retardation plate, or a prism sheet.

Electronic devices and lighting devices can be manufactured by using thedisplay panel, the light-emitting panel, the sensor panel, the touchpanel, the touch panel module, the input device, the display device, orthe input/output device of one embodiment of the present invention.Highly reliable electronic devices and lighting devices with curvedsurfaces can be manufactured by using the input device, the displaydevice, or the input/output device of one embodiment of the presentinvention. In addition, flexible and highly reliable electronic devicesand lighting devices can be manufactured by using the input device, thedisplay device, or the input/output device of one embodiment of thepresent invention. Furthermore, electronic devices and lighting devicesincluding touch sensors with improved sensitivity can be manufactured byusing the input device or the input/output device of one embodiment ofthe present invention.

Examples of electronic devices include a television set (also referredto as a television or a television receiver), a monitor of a computer orthe like, a digital camera, a digital video camera, a digital photoframe, a mobile phone (also referred to as a mobile phone device), aportable game machine, a portable information terminal, an audioreproducing device, and a large game machine such as a pachinko machine.

In the case of having flexibility, the electronic device or the lightingdevice of one embodiment of the present invention can be incorporatedalong a curved inside/outside wall surface of a house or a building or acurved interior/exterior surface of a car.

Furthermore, the electronic device of one embodiment of the presentinvention may include a secondary battery. Preferably, the secondarybattery is capable of being charged by contactless power transmission.

Examples of the secondary battery include a lithium ion battery such asa lithium polymer battery (lithium ion polymer battery) using a gelelectrolyte, a nickel-hydride battery, a nickel-cadmium battery, anorganic radical battery, a lead-acid battery, an air battery, anickel-zinc battery, and a silver-zinc battery.

The electronic device of one embodiment of the present invention mayinclude an antenna. When a signal is received by the antenna, an image,data, or the like can be displayed on a display portion. When theelectronic device includes a secondary battery, the antenna may be usedfor contactless power transmission.

FIGS. 24A to 24H and FIGS. 25A and 25B illustrate electronic devices.These electronic devices can each include a housing 5000, a displayportion 5001, a speaker 5003, an LED lamp 5004, operation keys 5005(including a power switch or an operation switch), a connection terminal5006, a sensor 5007 (a sensor having a function of measuring force,displacement, position, speed, acceleration, angular velocity,rotational frequency, distance, light, liquid, magnetism, temperature,chemical substance, sound, time, hardness, electric field, current,voltage, electric power, radiation, flow rate, humidity, gradient,oscillation, odor, or infrared rays), a microphone 5008, and the like.

FIG. 24A illustrates a mobile computer, which can include a switch 5009,an infrared port 5010, and the like in addition to the above components.

FIG. 24B illustrates a portable image reproducing device provided with arecording medium (e.g., a DVD reproducing device), which can include asecond display portion 5002, a recording medium reading portion 5011,and the like in addition to the above components.

FIG. 24C illustrates a television device, which can include a stand 5012and the like in addition to the above components. The television devicecan be operated by an operation switch of the housing 5000 or a separateremote controller 5013. With operation keys of the remote controller5013, channels and volume can be controlled, and images displayed on thedisplay portion 5001 can be controlled. The remote controller 5013 maybe provided with a display portion for displaying data output from theremote controller 5013.

FIG. 24D illustrates a portable game machine, which can include therecording medium reading portion 5011 and the like in addition to theabove components.

FIG. 24E illustrates a digital camera that has a television receptionfunction and can include an antenna 5014, a shutter button 5015, animage receiving portion 5016, and the like in addition to the abovecomponents.

FIG. 24F illustrates a portable game machine, which can include thesecond display portion 5002, the recording medium reading portion 5011,and the like in addition to the above components.

FIG. 24G illustrates a portable television receiver, which can include acharger 5017 capable of transmitting and receiving signals, and the likein addition to the above components.

FIG. 24H illustrates a wrist-watch-type information terminal, which caninclude a band 5018, a clasp 5019, and the like in addition to the abovecomponents. The display portion 5001 mounted in the housing 5000 alsoserving as a bezel includes a non-rectangular display region. Thedisplay portion 5001 can display an icon 5020 indicating time, anothericon 5021, and the like.

FIG. 25A illustrates a digital signage. FIG. 25B illustrates a digitalsignage mounted on a cylindrical pillar.

The electronic devices illustrated in FIGS. 24A to 24H and FIGS. 25A and25B can have a variety of functions, for example, a function ofdisplaying a variety of information (e.g., a stilt image, a movingimage, and a text image) on a display portion, a touch panel function, afunction of displaying a calendar, date, time, and the like, a functionof controlling processing with a variety of software (programs), awireless communication function, a function of being connected to avariety of computer networks with a wireless communication function, afunction of transmitting and receiving a variety of data with a wirelesscommunication function, and a function of reading a program or datastored in a recording medium and displaying the program or data on adisplay portion. Furthermore, the electronic device including aplurality of display portions can have a function of displaying imageinformation mainly on one display portion while displaying textinformation mainly on another display portion, a function of displayinga three-dimensional image by displaying images where parallax isconsidered on a plurality of display portions, or the like. Furthermore,the electronic device including an image receiving portion can have afunction of photographing a still image, a function of photographing amoving image, a function of automatically or manually correcting aphotographed image, a function of storing a photographed image in arecording medium (an external recording medium or a recording mediumincorporated in the camera), a function of displaying a photographedimage on a display portion, or the like. Note that the functions of theelectronic devices illustrated in FIGS. 24A to 24H and FIGS. 25A and 25Bare not limited thereto, and the electronic devices can have a varietyof functions.

FIGS. 26A, 26B, 26C1, 26C2, 26D, and 26E illustrate examples of anelectronic device including a display portion 7000 with a curvedsurface. The display surface of the display portion 7000 is bent, andimages can be displayed on the bent display surface. The display portion7000 may have flexibility.

The display portion 7000 can be formed using the functional panel, thedisplay panel, the light-emitting panel, the sensor panel, the touchpanel, the display device, the input/output device, or the like of oneembodiment of the present invention. One embodiment of the presentinvention makes it possible to provide a highly reliable electronicdevice having a curved display portion.

FIG. 26A illustrates an example of a mobile phone. A mobile phone 7100includes a housing 7101, the display portion 7000, operation buttons7103, an external connection port 7104, a speaker 7105, a microphone7106, and the like.

The mobile phone 7100 illustrated in FIG. 26A includes a touch sensor inthe display portion 7000. Operations such as making a call and inputtinga letter can be performed by touch on the display portion 7000 with afinger, a stylus, or the like.

With the operation buttons 7103, power ON or OFF can be switched. Inaddition, types of images displayed on the display portion 7000 can beswitched; for example, switching from a mail creation screen to a mainmenu screen can be performed.

FIG. 26B illustrates an example of a television set. In a television set7200, the display portion 7000 is incorporated into a housing 7201.Here, the housing 7201 is supported by a stand 7203.

The television set 7200 illustrated in FIG. 26B can be operated with anoperation switch of the housing 7201 or a separate remote controller7211. The display portion 7000 may include a touch sensor, and can beoperated by touch on the display portion 7000 with a finger or the like.The remote controller 7211 may be provided with a display portion fordisplaying data output from the remote controller 7211. With operationkeys or a touch panel of the remote controller 7211, channels and volumecan be controlled and images displayed on the display portion 7000 canbe controlled.

Note that the television set 7200 is provided with a receiver, a modem,and the like. A general television broadcast can be received with thereceiver. When the television set is connected to a communicationnetwork with or without wires via the modem, one-way (from a transmitterto a receiver) or two-way (between a transmitter and a receiver orbetween receivers) data communication can be performed.

FIGS. 26C1, 26C2, 26D, and 26E illustrate examples of a portableinformation terminal. Each of the portable information terminalsincludes a housing 7301 and the display portion 7000. Each of theportable information terminals may also include an operation button, anexternal connection port, a speaker, a microphone, an antenna, abattery, or the like. The display portion 7000 is provided with a touchsensor. An operation of the portable information terminal can beperformed by touch on the display portion 7000 with a finger, a stylus,or the like.

FIG. 26C1 is a perspective view of a portable information terminal 7300.FIG. 26C2 is a top view of the portable information terminal 7300. FIG.26D is a perspective view of a portable information terminal 7310. FIG.26E is a perspective view of a portable information terminal 7320.

Each of the portable information terminals illustrated in thisembodiment functions as, for example, one or more of a telephone set, anotebook, and an information browsing system. Specifically, the portableinformation terminals each can be used as a smartphone. Each of theportable information terminals illustrated in this embodiment is capableof executing, for example, a variety of applications such as mobilephone calls, e-mailing, reading and editing texts, music reproduction,Internet communication, and a computer game.

The portable information terminals 7300, 7310, and 7320 can displaycharacters and image information on its plurality of surfaces. Forexample, as illustrated in FIGS. 26C1 and 26D, three operation buttons7302 can be displayed on one surface, and information 7303 indicated bya rectangle can be displayed on another surface. FIGS. 26C1 and 26C2illustrate an example in which information is displayed at the top ofthe portable information terminal. FIG. 26D illustrates an example inwhich information is displayed on the side of the portable informationterminal. Information may be displayed on three or more surfaces of theportable information terminal. FIG. 26E shows an example in whichinformation 7304, information 7305, and information 7306 are displayedon different surfaces.

Examples of the information include notification from a socialnetworking service (SNS), display indicating reception of an e-mail oran incoming call, the title of an e-mail or the like, the sender of ane-mail or the like, the date, the time, remaining battery, and thereception strength of an antenna. Alternatively, the operation button,an icon, or the like may be displayed instead of the information.

For example, a user of the portable information terminal 7300 can seethe display (here, the information 7303) on the portable informationterminal 7300 put in a breast pocket of his/her clothes.

Specifically, a caller's phone number, name, or the like of an incomingcall is displayed in a position that can be seen from above the portableinformation terminal 7300. Thus, the user can see the display withouttaking out the portable information terminal 7300 from the pocket anddecide whether to answer the call.

FIGS. 26F to 26H each illustrate an example of a lighting device havinga curved light-emitting portion.

The light-emitting portion included in each of the lighting devicesillustrated in FIGS. 26F to 26H can be manufactured using the functionalpanel, the display panel, the light-emitting panel, the sensor panel,the touch panel, the display device, the input/output device, or thelike of one embodiment of the present invention. According to oneembodiment of the present invention, a highly reliable lighting devicehaving a curved light-emitting portion can be provided.

A lighting device 7400 illustrated in FIG. 26F includes a light-emittingportion 7402 with a wave-shaped light-emitting surface and thus is agood-design lighting device.

A light-emitting portion 7412 included in a lighting device 7410illustrated in FIG. 26G has two convex-curved light-emitting portionssymmetrically placed. Thus, all directions can be illuminated with thelighting device 7410 as a center.

A lighting device 7420 illustrated in FIG. 26H includes a concave-curvedlight-emitting portion 7422. This is suitable for illuminating aspecific range because light emitted from the light-emitting portion7422 is collected to the front of the lighting device 7420. In addition,with this structure, a shadow is less likely to be produced.

The light-emitting portion included in each of the lighting devices7400, 7410 and 7420 may have flexibility. The light-emitting portion maybe fixed on a plastic member, a movable frame, or the like so that alight-emitting surface of the light-emitting portion can be bent freelydepending on the intended use.

The lighting devices 7400, 7410, and 7420 each include a stage 7401provided with an operation switch 7403 and the light-emitting portionsupported by the stage 7401.

Note that although the lighting device in which the light-emittingportion is supported by the stage is described as an example here, ahousing provided with a light-emitting portion can be fixed on a ceilingor suspended from a ceiling. Since the light-emitting surface can becurved, the light-emitting surface is curved to have a concave shape,whereby a particular region can be brightly illuminated, or thelight-emitting surface is curved to have a convex shape, whereby a wholeroom can be brightly illuminated.

FIGS. 27A1, 27A2, and 27B to 271 each illustrate an example of aportable information terminal including a display portion 7001 havingflexibility.

The display portion 7001 is manufactured using the functional panel, thedisplay panel, the light-emitting panel, the sensor panel, the touchpanel, the display device, the input/output device, or the like of oneembodiment of the present invention. For example, a display device or aninput/output device that can be bent with a radius of curvature ofgreater than or equal to 0.01 mm and less than or equal to 150 mm can beused. The display portion 7001 may include a touch sensor so that theportable information terminal can be operated by touch on the displayportion 7001 with a finger or the like. One embodiment of the presentinvention makes it possible to provide a highly reliable electronicdevice including a display portion having flexibility.

FIGS. 27A1 and 27A2 are a perspective view and a side view illustratingan example of the portable information terminal. A portable informationterminal 7500 includes a housing 7501, the display portion 7001, adisplay portion tab 7502, operation buttons 7503, and the like.

The portable information terminal 7500 includes a rolled flexibledisplay portion 7001 in the housing 7501.

The portable information terminal 7500 can receive a video signal with acontrol portion incorporated therein and can display the received imageon the display portion 7001. The portable information terminal 7500incorporates a battery. A terminal portion for connecting a connectormay be included in the housing 7501 so that a video signal or power canbe directly supplied from the outside with a wiring.

By pressing the operation buttons 7503, power ON/OFF, switching ofdisplayed images, and the like can be performed. Although FIGS. 27A1,27A2, and 27B show an example in which the operation buttons 7503 arepositioned on a side surface of the portable information terminal 7500,one embodiment of the present invention is not limited thereto. Theoperation buttons 7503 may be placed on a display surface (a frontsurface) or a rear surface of the portable information terminal 7500.

FIG. 27B illustrates the portable information terminal 7500 in a statewhere the display portion 7001 is pulled out with the display portiontab 7502. Images can be displayed on the display portion 7001 in thisstate. In addition, the portable information terminal 7500 may performdifferent displays in the state where part of the display portion 7001is rolled as shown in FIG. 27A1 and in the state where the displayportion 7001 is pulled out with the display portion tab 7502 as shown inFIG. 27B. For example, in the state shown in FIG. 27A1, the rolledportion of the display portion 7001 is put in a non-display state,reducing the power consumption of the portable information terminal7500.

Note that a reinforcement frame may be provided for a side portion ofthe display portion 7001 so that the display portion 7001 has a flatdisplay surface when pulled out.

Note that in addition to this structure, a speaker may be provided forthe housing so that sound is output with an audio signal receivedtogether with a video signal.

FIGS. 27C to 27E illustrate an example of a foldable portableinformation terminal. FIG. 27C illustrates a portable informationterminal 7600 that is opened. FIG. 27D illustrates the portableinformation terminal 7600 that is being opened or being folded. FIG. 27Eillustrates the portable information terminal 7600 that is folded. Theportable information terminal 7600 is highly portable when folded, andis highly browsable when opened because of a seamless large displayarea.

The display portion 7001 is supported by three housings 7601 joinedtogether by hinges 7602. By folding the portable information terminal7600 at a connection portion between two housings 7601 with the hinges7602, the portable information terminal 7600 can be reversibly changedin shape from an opened state to a folded state.

FIGS. 27F and 27G illustrate an example of a foldable portableinformation terminal. FIG. 27F illustrates a portable informationterminal 7650 that is folded so that the display portion 7001 is on theinside. FIG. 27G illustrates the portable information terminal 7650 thatis folded so that the display portion 7001 is on the outside. Theportable information terminal 7650 includes the display portion 7001 anda non-display portion 7651. When the portable information terminal 7650is not used, the portable information terminal 7650 is folded so thatthe display portion 7001 is on the inside, whereby the display portion7001 can be prevented from being contaminated or damaged.

FIG. 27H illustrates an example of a flexible portable informationterminal. A portable information terminal 7700 includes a housing 7701and the display portion 7001. The portable information terminal 7700 mayfurther include buttons 7703 a and 7703 b which serve as input means,speakers 7704 a and 7704 b which serve as sound output means, anexternal connection port 7705, a microphone 7706, or the like. Aflexible battery 7709 can be included in the portable informationterminal 7700. The battery 7709 may be arranged to overlap with thedisplay portion 7001, for example.

The housing 7701, the display portion 7001, and the battery 7709 haveflexibility. Thus, it is easy to curve the portable information terminal7700 into a desired shape or to twist the portable information terminal7700. For example, the portable information terminal 7700 can be foldedso that the display portion 7001 is on the inside or on the outside. Theportable information terminal 7700 can be used in a rolled state. Sincethe housing 7701 and the display portion 7001 can be transformed freelyin this manner, the portable information terminal 7700 is less likely tobe broken even when the portable information terminal 7700 falls down orexternal stress is applied to the portable information terminal 7700.

The portable information terminal 7700 is lightweight and therefore canbe used conveniently in various situations. For example, the portableinformation terminal 7700 can be used in the state where the upperportion of the housing 7701 is suspended by a clip or the like, or inthe state where the housing 7701 is fixed to a wall by magnets or thelike.

FIG. 271 illustrates an example of a wrist-watch-type portableinformation terminal. The portable information terminal 7800 includes aband 7801, the display portion 7001, an input/output terminal 7802,operation buttons 7803, and the like. The band 7801 has a function as ahousing. A flexible battery 7805 can be included in the portableinformation terminal 7800. The battery 7805 may be arranged to overlapwith the display portion 7001 and the band 7801, for example.

The band 7801, the display portion 7001, and the battery 7805 haveflexibility. Thus, the portable information terminal 7800 can be easilycurved to have a desired shape.

With the operation buttons 7803, a variety of functions such as timesetting, ON/OFF of the power, ON/OFF of wireless communication, settingand cancellation of silent mode, and setting and cancellation of powersaving mode can be performed. For example, the functions of theoperation buttons 7803 can be set freely by the operating systemincorporated in the portable information terminal 7800.

By touch on an icon 7804 displayed on the display portion 7001 with afinger or the like, application can be started.

The portable information terminal 7800 can employ near fieldcommunication conformable to a communication standard. For example,mutual communication between the portable information terminal and aheadset capable of wireless communication can be performed, and thushands-free calling is possible.

The portable information terminal 7800 may include the input/outputterminal 7802. In the case where the input/output terminal 7802 isincluded in the portable information terminal 7800, data can be directlytransmitted to and received from another information terminal via aconnector. Charging through the input/output terminal 7802 is alsopossible. Note that charging of the portable information terminaldescribed as an example in this embodiment can be performed bycontactless power transmission without using the input/output terminal.

FIGS. 28A to 28C illustrate an example of a watch-type foldable portableinformation terminal. A portable information terminal 7900 includes adisplay portion 7901, a housing 7902, a housing 7903, a band 7904, anoperation button 7905, and the like.

The portable information terminal 7900 can be reversibly changed inshape from a state in which the housing 7902 overlaps with the housing7903 as illustrated in FIG. 28A into a state in which the displayportion 7901 is opened as illustrated in FIG. 28C by lifting the housing7902 as illustrated in FIG. 28B. Therefore, the portable informationterminal 7900 can be generally used in a state where the display portion7901 is folded and can be used with a wide display region by developingthe display portion 7901.

When the display portion 7901 functions as a touch panel, the portableinformation terminal 7900 can be operated by touch on the displayportion 7901. The portable information terminal 7900 can be operated bypushing, turning, or sliding the operation button 7905 vertically,forward, or backward.

A lock mechanism is preferably provided so that the housing 7902 and thehousing 7903 are not detached from each other accidentally whenoverlapping with each other as illustrated in FIG. 28A. In that case,preferably, the lock state can be canceled by pushing the operationbutton 7905, for example. Alternatively, the lock state may be canceledby utilizing restoring force of a spring or the like as a mechanism inwhich the portable information terminal is automatically changed in formfrom the state illustrated in FIG. 28A into the state illustrated inFIG. 28C. Alternatively, the position of the housing 7902 relative tothe housing 7903 may be fixed by utilizing magnetic force instead of thelock mechanism. By utilizing magnetic force, the housing 7902 and thehousing 7903 can be easily attached or detached.

Although the display portion 7901 can be opened in a directionsubstantially perpendicular to the bending direction of the band 7904 inFIGS. 28A to 28C, the display portion 7901 may be opened in a directionsubstantially parallel to the bending direction of the band 7904 asillustrated in FIGS. 28D and 28E. In that case, the display portion 7901may be used in a bent state to be wound to the band 7904.

The electronic devices described in this embodiment each include adisplay portion for displaying some kind of information. The displaydevice such as the display panel, the touch panel, or the touch panelmodule of one embodiment of the present invention can be used for thedisplay portion.

At least part of this embodiment can be implemented in combination withany of the other embodiments described in this specification asappropriate.

EXAMPLE

A display device of one embodiment of the present invention wasfabricated, and the observation results of the cross section thereofwill be described below. For the cross-sectional structure of thedisplay device fabricated in this example, FIG. 9 can be referred to.

[Fabrication of Display Device]

First, a transistor, a wiring connected to the transistor, and the likewere formed over a glass substrate. As the transistor (the transistor201, 202, 205, or the like), a bottom-gate transistor using an oxidesemiconductor for a semiconductor where a channel was formed wasemployed. In this example, a crystalline oxide semiconductor havingc-axis alignment in a direction perpendicular to a film surface(CAAC-OS: c-axis aligned crystalline-oxide semiconductor) was used asthe oxide semiconductor.

The CAAC-OS is a crystalline oxide semiconductor in which c-axes ofcrystals are oriented in a direction substantially perpendicular to thefilm surface. It has been found that oxide semiconductors have a varietyof crystal structures other than a single crystal structure. An exampleof such structures is a nano-crystal (nc) structure, which is anaggregate of nanoscale microcrystals. The crystallinity of a CAAC-OSstructure is lower than that of a single crystal structure and higherthan that of an nc structure. Since the CAAC-OS does not have a grainboundary, a stable and uniform film can be formed over a large area, andstress that is caused by bending a flexible light-emitting device doesnot easily make a crack in a CAAC-OS film.

In this example, In—Ga—Zn-based oxide was used as the oxidesemiconductor material

Subsequently, a first electrode serving as a pixel electrode was formedover an insulating layer covering the transistor, the wiring, and thelike. The first electrode has a layered structure of a titanium film, analuminum film, and a titanium film. Then, an insulating layer coveringan end portion of the first electrode was formed. The insulating layerwas formed using photosensitive polyimide with a thickness ofapproximately 2 μm. After that, a structure body was formed over theinsulating layer using photosensitive polyimide with a thickness ofapproximately 1.25 μm.

Then, an EL layer and a second electrode were deposited by anevaporation method, whereby a light-emitting element was obtained. Here,the EL layer and the second electrode were formed over an entire displayregion without using a metal mask.

A light-blocking layer was formed over another glass substrate. A blackmatrix with a thickness of approximately 0.6 μm was used as thelight-blocking layer. Subsequently, a red coloring layer (R), a greencoloring layer (G), and a blue coloring layer (B) were formed to athickness of approximately 2.0 μm, a thickness of approximately 1.5 μm,and a thickness of approximately 1.5 μm, respectively.

Then, the two glass substrates were attached with an adhesive, and theadhesive was cured. The adhesive was formed by screen printing on thesubstrate provided with the coloring layers. A thermosetting epoxy wasused for the adhesive. The substrates were attached under areduced-pressure atmosphere.

White was displayed on the entire display region of the display devicefabricated in this example, and the display surface was visuallyobserved perpendicularly and obliquely. As a result, an extremely smallchange in chromaticity and luminance was found even when the displaysurface was seen obliquely.

[Cross-Sectional Observation Results]

The fabricated display device was processed by ion milling and the crosssection thereof was observed by scanning electron microscope (SEM).

FIGS. 29A and 29B show observed cross-sectional images. FIGS. 29A and29B show the same image; in FIG. 29B, the outline of each layer in FIG.29A is denoted by a dashed line for clarity.

Note that holes found in part of the EL layer in FIGS. 29A and 29B wereformed in the processing for the cross-sectional observation.

FIGS. 29A and 29B show two structure bodies: the left one is positionedbetween the coloring layer (R) and the coloring layer (B), and the rightone is positioned between the coloring layer (R) and the coloring layer(G). In each of the structure bodies, a portion positioned on an upperside than the bottom surface of the coloring layer (R) was found.

In the fabricated display device, a region in which the distance betweenthe first electrode and the coloring layer (R) (a difference in theheight therebetween) was approximately 1.0 μm was found in the openingin the insulating layer. A region in which the distance between thesecond electrode and the coloring layer (R) was approximately 0.7 μm wasalso found in the opening in the insulating layer. In addition, a regionin which the distance between the first electrode and the light-blockinglayer was approximately 2.8 μm was found in the opening in theinsulating layer. Furthermore, a region in which the distance betweenthe second electrode and the light-blocking layer was approximately 2.5μm was found in the opening in the insulating layer.

The display device was found to have a region in which the distancebetween the structure body and the light-blocking layer wasapproximately 1.5 μm. It was also found that the distance between thesecond electrode and the light-blocking layer over the structure bodywas approximately 1.2 μm.

The structure body had an inverse tapered shape with a taper angle (theangle between the bottom surface and the side surface of the structurebody) of approximately 45° to 70°. Part of the EL layer covering thestructure body was found to be thinner than another part of the EL layerover the first electrode.

The above results showed that the display device fabricated in thisexample had an extremely small distance between the pair of substrates.Moreover, improved viewing angle characteristics were observed visually.

The above is the description of this example.

This application is based on Japanese Patent Application serial No.2015-169163 filed with Japan Patent Office on Aug. 28, 2015, andJapanese Patent Application serial No. 2016-119610 filed with JapanPatent Office on Jun. 16, 2016, the entire contents of which are herebyincorporated by reference.

EXPLANATION OF REFERENCE

10: display device 11: structure body 11 a: portion 12: structure body21: substrate 23: conductive layer 24: EL layer 24 a: EL layer 24 b: Ellayer 25: conductive layer 31: substrate 32: display portion 34: circuit35: wiring 39: adhesive layer 40: light-emitting element 42: FPC 43: IC51: coloring layer 51 a: coloring layer 51 b: coloring layer 51 c:coloring layer 52: light-blocking layer 52 b: coloring layer 60: liquidcrystal element 61: conductive layer 62: liquid crystal 63: conductivelayer 64: insulating layer 65: insulating layer 70: transistor 71:conductive layer 72: semiconductor layer 73: insulating layer 74 a:conductive layer 74 b: conductive layer 81: insulating layer 81 a:insulating layer 81 b: insulating layer 82: insulating layer 82 a:portion 90: transistor 91: single crystal substrate 95 a: connectionlayer 95 b: connection layer 96: conductive layer 100: touch panel 111:conductive layer 112: EL layer 113: conductive layer 130: polarizingplate 131: coloring layer 131 a: coloring layer 131 b: coloring layer132: light-blocking layer 133: light-blocking layer 134: coloring layer141: adhesive layer 142: adhesive layer 146: conductive film 147:conductive film 148: conductive film 149: nanowire 150: input device151: electrode 152: electrode 153: bridge electrode 155: wiring 157: FPC150: IC 160: substrate 161: insulating layer 162: insulating layer 163:insulating layer 164: insulating layer 165: adhesive layer 168: IC 169:connection portion 170: substrate 171: substrate 172: adhesive layer173: insulating layer 181: substrate 183: insulating layer 191:conductive layer 192: conductive layer 192: liquid crystal 194:conductive layer 195: insulating layer 200: display device 201:transistor 202: transistor 203: capacitor 204: terminal portion 205:transistor 206: transistor 206:

terminal portion 210: pixel 211: insulating layer 212: insulating layer213: insulating layer 214: insulating layer 215: insulating layer 216:insulating layer 220: insulating layer 221: conductive layer 222:conductive layer 223: conductive layer 224: conductive layer 231:semiconductor layer 242: connection layer 243: connector 251: opening252: connection portion 601: pulse voltage output circuit 602: currentsensing circuit 603: capacitor 621: electrode 622: electrode 705:insulating layer 706: electrode 707: insulating layer 708: semiconductorlayer 710: insulating layer 711: insulating layer 714: electrode 715:electrode 722: insulating layer 723: electrode 726: insulating layer727: insulating layer 728: insulating layer 729: insulating layer 741:insulating layer 742: semiconductor layer 744a: electrode 744b:electrode 746: electrode 755: impurity 771: substrate 772: insulatinglayer 810: transistor 811: transistor 820: transistor 821: transistor825: transistor 830: transistor 831: transistor 840: transistor 841:transistor 842: transistor 843: transistor 844: transistor 845:transistor 846: transistor 847: transistor 5000: housing 5001: displayportion 5002: display portion 5003: speaker 5004: LED lamp 5005:operation key 5006: connection terminal 5007: sensor 5008: microphone5009: switch 5010: infrared port 5011: recording medium reading portion5012: stand 5013: remote controller 5014: antenna 5015: shutter button5016: image receiving portion 5017: charger 5018: band 5019: clasp 5020:icon 5021: icon 7000: display portion 7001: display portion 7100: mobilephone 7101: housing 7103: operation button 7104: external connectionport 7105: speaker 7106: microphone 7200: television set 7201: housing7203: stand 7211: remote controller 7300: portable information terminal7301: housing 7302: operation button 7303: information 7304: information7305: information 7306: information 7310: portable information terminal7320: portable information terminal 7400: lighting device 7401: stage7402: light-emitting portion 7403: operation switch 7410: lightingdevice 7412: light-emitting portion 7420: lighting device 7422:light-emitting portion 7500: portable information terminal 7501: housing7502: member 7503: operation button 7600: portable information terminal7601: housing 7602: hinge 7650: portable information terminal 7651:non-display portion 7700: portable information terminal 7701: housing7703 a: button 7703 b: button 7704 a: speaker 7704 b: speaker 7705:external connection port 7706: microphone 7709: battery 7800: portableinformation terminal 7801: band 7802: input/output terminal 7803:operation button 7804: icon 7805: battery 7900: portable informationterminal 7901: display portion 7902: housing 7903: housing 7904: band7905: operation button 8000: display module 8001: upper cover 8002:lower cover 8003: FPC 8004: touch panel 8009: frame 8010: printed board8011: battery

What is claimed is:
 1. A display device comprising: an insulating layerover a first substrate; a first coloring layer and a second coloringlayer over the insulating layer; a structure body over and in directlycontact with the insulating layer, and between the first coloring layerand the second coloring layer; and a second substrate over the firstcoloring layer and the second coloring layer, wherein a top surface ofthe structure body is closer to the second substrate side than a bottomsurface of the first coloring layer or a bottom surface of the secondcoloring layer is.
 2. The display device according to claim 1, wherein athickness of the first coloring layer is different from a thickness ofthe second coloring layer.
 3. The display device according to claim I.wherein a top surface of the first coloring layer and a top surface ofthe second coloring layer are closer to the second substrate side thanthe bottom surface of the first coloring layer and the bottom surface ofthe second coloring layer.
 4. The display device according to claim 1,further comprising: a first transistor overlapping with the firstcoloring layer; and a second transistor overlapping with the secondcoloring layer.
 5. The display device according to claim I, furthercomprising: a first display element overlapping with the first coloringlayer; and a second display element overlapping with the second coloringlayer.
 6. The display device according to claim 5, wherein each of thefirst display element and the second display element is a light-emittingelement.
 7. The display device according to claim I, wherein the firstcoloring layer and the second coloring layer are apart from each other.8. The display device according to claim 1, wherein the structure bodyand the second substrate overlap each other with an adhesive layertherebetween.